Display device, method of manufacturing display device, and electronic apparatus

ABSTRACT

A display device according to the present disclosure includes: a thin film transistor with a bottom gate structure and a thin film transistor with a top gate structure on a same substrate. A gate electrode of the thin film transistor with the top gate structure is provided in a same layer as a wire layer. A method of manufacturing a display device according to the present disclosure, the display device including a thin film transistor with a bottom gate structure and a thin film transistor with a top gate structure on a same substrate, includes: forming a gate electrode of the thin film transistor with the top gate structure in a same layer as a wire layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 16/714,254,filed Dec. 13, 2019, which is a Continuation of application Ser. No.16/380,522, filed Apr. 10, 2019, now U.S. Pat. No. 10,535,723 issued onJan. 14, 2020, which is a Continuation of application Ser. No.16/226,130, filed Dec. 19, 2018, now U.S. Pat. No. 10,573,700 issued onFeb. 25, 2020, which is a Continuation of application Ser. No.15/323,651, filed Jan. 3, 2017, now U.S. Pat. No. 10,297,653 issued onMay 21, 2019, which is a U.S. National Phase of International PatentApplication No. PCT/JP2015/061962 filed on Apr. 20, 2015, which claimspriority benefit of Japanese Patent Application No. JP 2014-149433 filedin the Japan Patent Office on Jul. 23, 2014. Each of theabove-referenced applications is hereby incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present disclosure relates to a display device, a method ofmanufacturing display device, and an electronic apparatus, andparticularly, to a plane type (flat panel type) display device, a methodof manufacturing the display device, and an electronic apparatusincluding the display device.

BACKGROUND ART

Liquid crystal display (LCD) devices or organic electro luminescence(EL) display devices are known as plane type display devices (flatdisplays). In addition, As one of the driving methods of the plane typedisplay devices, there is an active-matrix method. In active-matrixdisplay devices, thin film transistors (TFT) are generally used asactive elements driving light emission units (light emission elements)of pixels.

As basic performances necessary in thin film transistors (which will bealso described hereinafter as “TFTs” in some cases), a large drivingcurrent at the time of writing of a signal, a small leakage current atthe time of retaining of a signal, and a small variation incharacteristics between elements can be exemplified. On the other hand,performance values necessary in pixel control TFTs and peripheralcircuit control TFTs are not necessarily the same, but there areappropriate values. Therefore, it is necessary to separately generateelement characteristics between the pixel control TFTs and theperipheral circuit control TFTs. This point is also similar between TFTswhen a pixel circuit is configured using the plurality of TFTs inpixels.

In the related art, element characteristics of TFTs are separatelygenerated by changing densities of ion implantation of the TFTs betweena display region in which pixels are formed and a peripheral region inwhich peripheral circuits are formed (for example, see Patent Literature1).

CITATION LIST Patent Literature

Patent Literature 1: JP H9-45931A

DISCLOSURE OF INVENTION Technical Problem

However, in technologies of the related art, in order to changedensities of ion implantation, it is necessary to add processes.Accordingly, since costs increase accompanying the processes beingadded, there is a disadvantage in cost competitiveness.

According to the present disclosure, an object of the present disclosureis to provide a display device in which element characteristics are ableto be separately generated without adding processes, a method ofmanufacturing the display device, and an electronic apparatus includingthe display device.

Solution to Problem

In order to achieve the object, a display device according to thepresent disclosure includes: a thin film transistor with a bottom gatestructure and a thin film transistor with a top gate structure on a samesubstrate. A gate electrode of the thin film transistor with the topgate structure is provided in a same layer as a wire layer.

In order to achieve the object, a method of manufacturing a displaydevice according to the present disclosure, the display device includinga thin film transistor with a bottom gate structure and a thin filmtransistor with a top gate structure on a same substrate, includes:forming a top gate electrode of the thin film transistor with the topgate structure in a same layer as a wire layer.

In order to achieve the object, an electronic apparatus according to thepresent disclosure includes: a display device which includes a thin filmtransistor with a bottom gate structure and a thin film transistor witha top gate structure on a same substrate and in which a top gateelectrode of the thin film transistor with the top gate structure isprovided in a same layer as a wire layer.

Advantageous Effects of Invention

According to the present disclosure, element characteristics are able tobe separately generated in a structure without adding processes sincethe same layer as a wire layer is used as a gate electrode of a thinfilm transistor with a top gate structure.

Note that the present disclosure is not limited to exhibiting the effectdescribed herein at all and may exhibit any effect described in thepresent specification. In addition, the effects described in the presentspecification are not limiting but are merely examples, and there may beadditional effects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system configuration diagram showing a schematic basicconfiguration of an active-matrix display device to which the technologyof the present disclosure is applied.

FIG. 2 is a circuit diagram showing an example of a detailed circuitconfiguration of a unit pixel (pixel circuit).

FIG. 3 is a sectional view showing a TFT structure according to Example1.

FIG. 4 is a plan view showing the TFT structure according to Example 1.

FIGS. 5A to 5C are process diagrams showing a procedure of a method ofmanufacturing the TFT structure according to Example 1.

FIG. 6 is a characteristic diagram showing an example of elementcharacteristics of a TFT with a bottom gate structure and a TFT with atop gate structure.

FIG. 7A is a plan view showing disposition when both of a drivetransistor and a writing transistor are constituted by TFTs with thebottom gate structure and FIG. 7B is a plan view showing dispositionwhen the drive transistor is constituted by a TFT with the top gatestructure and the writing transistor is constituted by a TFT with thebottom gate structure.

FIG. 8A is a plan view showing a TFT structure according to Example 2and FIG. 8B is a plan view showing a TFT structure according to Example3.

FIG. 9 is a sectional view showing a TFT structure according to Example4.

FIG. 10 is a plan view showing the TFT structure according to Example 4.

FIGS. 11A and 11B are process diagrams showing a procedure of a methodof manufacturing the TFT structure according to Example 4.

FIG. 12A is a plan view showing a TFT structure according to Example 5and FIG. 12B is a plan view showing a TFT structure according to Example6.

FIG. 13A is a sectional view showing a TFT structure according toExample 7 and 13B is a sectional view showing a TFT structure accordingto Example 7.

FIG. 14A is a plan view showing a TFT structure according to Example 8and FIG. 14B is a plan view showing the TFT structure according toExample 8.

FIG. 15A is a plan view showing a TFT structure according to Example 9and FIG. 15B is a plan view showing the TFT structure according toExample 9.

FIG. 16 is a sectional view showing a TFT structure according to Example10.

FIG. 17 is a sectional view showing a TFT structure according to Example10.

FIG. 18 is a sectional view showing a TFT structure according to Example11.

FIG. 19 is a sectional view showing a TFT structure according to Example11.

FIGS. 20A to 20C are process diagrams showing a procedure of a method ofmanufacturing the TFT structure according to Example 11.

FIGS. 21A and 21B are external views showing smartphones which areexamples of electronic apparatuses according to the present disclosure.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments for implementing the technology ofthe present disclosure (which will be described hereinafter as“embodiments”) will be described in detail with reference to theappended drawings. The technology of the present disclosure is notlimited to the embodiments, and the various numeric values and materialsshown in the embodiments are examples. In description provided below,structural elements that have substantially the same function andstructure are denoted with the same reference numerals, and repeatedexplanation of these structural elements is omitted. Note thatdescription will be provided in the following order.

1. Overall description of display device, method of manufacturingdisplay device, and electronic apparatus according to present disclosure

2. Display device (which is example of organic EL, display device) towhich technology of present disclosure is applied

2-1. System configuration

2-2. Pixel circuit

2-3. Performance value (element characteristics) necessary in TFT

3. First embodiment

3-1. Example 1 [example in which wire layer has one-layer structure]

3-2. Example 2 [modification example of Example 1: series connection]

3-3. Example 3 [another modification example of Example 1: parallelconnection]

3-4. Example 4 [example in which wire layer has two-layer structure]

3-5. Example 5 [modification example of Example 4: series connection]

3-6. Example 6 [another modification example of Example 4: parallelconnection]

4. Second embodiment

4-1. Example 7 [example in which wiring CVD method is used: wire layerhas one-layer structure]

4-2. Example 8 [example in which redundant TFT is used]

4-3. Example 9 [modification example of Example 7: wire layer hastwo-layer structure]

4-4. Example 10 [another modification example of Example 7: parallelconnection]

5. Third embodiment

5-1. Example 11 [example in which TFT with top gate structure in whichTFT has no dummy gate electrode]

6. Electronic apparatus (example of smartphone)

<Overall Description of Display Device, Method of Manufacturing DisplayDevice, and Electronic Apparatus According to Present Disclosure>

In a display device, a method of manufacturing the display device, andan electronic apparatus according to the present disclosure, a top gateelectrode of a thin film transistor with a top gate structure can beconfigured to be integrated by extending from a wire electricallyconnected to a source/drain region of a thin film transistor with abottom gate structure. In addition, the thin film transistor with thetop gate structure can be configured to include a dummy gate electrodein a floating state without supplying a potential.

In the display device having the above-described preferredconfiguration, the method of manufacturing the display device, and theelectronic apparatus according to the present disclosure, a wire layerin which a top gate structure is provided can be configured to be afirst wire layer provided on an inter-layer insulation film on a thinfilm transistor. Alternatively, in a TFT structure in which the firstwire layer is provided on the inter-layer insulation film on the thinfilm transistor and a first inter-layer film is provided on the firstwire layer, a wire layer in which the top gate structure is provided canbe configured to be a second wire layer provided on the firstinter-layer film.

In addition, in the display device having the above-described preferredconfiguration, the method of manufacturing the display device, and theelectronic apparatus according to the present disclosure, in a TFTstructure in which a contact hole is formed in a site of the inter-layerinsulation film corresponding to a channel region of the thin filmtransistor with the top gate structure, a gate insulation film isprovided on the inter-layer insulation film containing the contact hole.The gate insulation film can be constituted by a high dielectricinter-layer film.

Alternatively, in the display device having the above-describedpreferred configuration, the method of manufacturing the display device,and the electronic apparatus according to the present disclosure, in aTFT structure in which the contact hole is formed in a site of the firstinter-layer film corresponding to the thin film transistor with the topgate structure, the top gate electrode of the thin film transistor withthe top gate structure can be provided in the same layer as a secondwire layer on the first inter-layer film, in the contact hole, and onthe gate insulation film.

In addition, in the display device having the above-described preferredconfiguration, the method of manufacturing the display device, and theelectronic apparatus according to the present disclosure, the thin filmtransistor with the bottom gate structure and the thin film transistorwith the top gate structure are connected in series for use.Alternatively, these thin film transistors are connected in parallel foruse. At this time, preferably, a source or drain region of the thin filmtransistor with the bottom gate structure is connected directly to asource or drain region of the thin film transistor with the top gatestructure without passing through a wire layer. In addition, preferably,a bottom gate electrode of the thin film transistor with the bottom gatestructure and the top gate electrode of the thin film transistor withthe top gate structure have a same potential.

Alternatively, in the display device having the above-describedpreferred configuration, the method of manufacturing the display device,and the electronic apparatus according to the present disclosure, a unitpixel including a light emission unit can be disposed to be constituted.The unit pixel can include a writing transistor that writes a signal anda drive transistor that drives the light emission unit based on thesignal written by the writing transistor. The writing transistor can beconstituted by the thin film transistor with the bottom gate structure.The drive transistor can be constituted by the thin film transistor withthe top gate structure.

Here, the light emission unit of the unit pixel can be constituted by acurrent-driven electro-optical element, for example, an organic electroluminescence (EL) element. The organic EL element is a self-luminouselement that uses a phenomenon in which light is emitted when anelectric field is applied to an organic thin film using an electroluminescence of an organic material. As the current-drivenelectro-optical element, not only an organic EL element but also aninorganic EL element, an LED element, a semiconductor laser element, orthe like can be exemplified.

The organic EL element has a configuration in which a hole transportlayer, a light emission layer, an electron transport layer, and anelectron injection layer are sequentially stacked on a first electrode(for example, an anode) to form an organic layer, and a second electrode(for example, a cathode) is formed on the organic layer. By applying adirect-current voltage between the first and second electrodes, light isemitted when holes pass through the hole transport layer from the firstelectrode (anode), electrons pass through the electron transport layerfrom the second electrode (cathode) and are injected into the lightemission layer, and the electrons and the holes are recombined in thelight emission layer.

An organic EL display device that uses organic EL elements as lightemission units of pixels has the following characteristics. Because theorganic EL elements can be driven with an applied voltage of 10 V orlower, the organic EL display device consumes low electric power. Sincethe organic EL elements are self-luminous elements, the organic ELdisplay device has higher visibility of images than a liquid crystaldisplay device, which is another display device of the same plane type,and even can be made lighter and thinner because no lighting member suchas a backlight or the like is necessary for the organic EL displaydevice. Furthermore, since a response speed of an organic EL element isabout several μsec, which is a very high speed, the organic EL displaydevice does not cause afterimages during display of dynamic images.

In another method of manufacturing the display device according to thepresent disclosure, an array test is performed to determine elementcharacteristics of an individual thin film transistor in a step offorming a thin film transistor with a bottom gate structure. A top gateelectrode is formed in a same layer as a wire layer in regard to thethin film transistor with the bottom gate structure in order to repair apixel including a thin film transistor determined to be worse thanpredetermined characteristics. At this time, the top gate electrode ispreferably formed using a technical method of connecting a wire byforming a metal thin film in accordance with a CVD method.

In still another method of manufacturing the display device includingthe above-described preferred configuration according to the presentdisclosure, when the thin film transistor in which the top gateelectrode is formed is a repairing target thin film transistordetermined to be worse than predetermined characteristics, the top gateelectrodes can be formed to face a bottom gate electrode of therepairing target thin film transistor with a channel region interposedtherebetween. Alternatively, when the thin film transistor in which thetop gate electrode is formed is another thin film transistor that isprovided on a same substrate as a repairing target thin film transistordetermined to be worse than predetermined characteristics and connectedin parallel to the repairing target thin film transistor, the top gateelectrodes can be formed to face a bottom gate electrode of the otherthin film transistor with a channel region interposed therebetween.

<Display Device to which the Technology of Present Disclosure isApplied>

[System Configuration]

FIG. 1 is a system configuration diagram showing a schematic basicconfiguration of an active-matrix display device to which the technologyof the present disclosure is applied.

The active-matrix display device is a display device in which driving ofa light emission unit (light emission element) is performed by an activeelement provided in the same pixel as the light emission unit, forexample, an insulated gate field-effect transistor. Typically, a thinfilm transistor (TFT) can be used as the insulated gate field-effecttransistor.

Here, a case in which an active-matrix organic EL display device uses anorganic EL element as a light emission unit (light emission element) ofa unit pixel (pixel circuit) will be described as an example. Theorganic El element is a current-driven electro-optical element of whichlight emission luminance changes according to a value of a currentflowing through the device. Hereinafter, the “unit pixel/pixel circuit”is described simply as a “pixel” in some cases. The thin film transistoris used not only for control of a pixel but also for control of aperipheral circuit to be described below.

As shown in FIG. 1, an organic EL display device 10 to which thetechnology of the present disclosure is applied is configured to includea pixel array unit 30 constituted such that a plurality of unit pixels20 are disposed 2-dimensionally in a matrix form (matrix state) and adriving unit (periphery) disposed in a peripheral region of the pixelarray unit 30 and driving pixels 20. The driving unit is constituted by,for example, a write scanning unit 40, a power supply scanning unit 50,and a signal output unit 60 and drives the pixels 20 of the pixel arrayunit 30. In this example, the write scanning unit 40, the power supplyscanning unit 50, and the signal output unit 60 are mounted on the samesubstrate as the pixel array unit 30, that is, a display panel 70. Here,it is also possible to employ a configuration in which some or all ofthe write scanning unit 40, the power supply scanning unit 50, and thesignal output unit 60 are provided out of the display panel 70.

Here, when the organic EL display device 10 displays in color, one pixel(unit pixel) serving as a unit forming a color image is constituted by aplurality of sub pixels. In this case, each of the sub pixelscorresponds to a pixel 20 of FIG. 1. To be more specific, in the displaydevice that displays in color, one pixel is constituted by, for example,three sub pixels including a sub pixel emitting red (R) light, a subpixel emitting green (G) light, and a sub pixel emitting blue (B) light.

One pixel, however, is not limited to a combination of sub pixels havingthree primary colors including RGB, and it is also possible to add subpixels having one or more colors to the sub pixels having the threeprimary colors to form one pixel. To be more specific, it is possible toform one pixel by adding a sub pixel that emits white (W) light toincrease luminance, or to form one pixel by adding at least one subpixel which emits a complementary color of light to expand a colorreproduction range.

In the pixel array unit 30, scanning lines 31 (31 ₁ to 31 _(m)) andpower supply lines 32 (32 ₁ to 32 _(m)) are wired for each pixel row inthe row direction (pixel array direction of pixel rows or horizontaldirection) in the array of the pixels 20 in m rows and n columns.Furthermore, signal lines 33 (33 ₁ to 33 _(n)) are wired for each pixelcolumn in the column direction (pixel array direction of pixel columnsor vertical direction) in the array of the pixels 20 in m rows and ncolumns.

The scanning lines 31 ₁ to 31 _(m) are connected to respective outputterminals of the rows corresponding to the write scanning unit 40. Thepower supply lines 32 ₁ to 32 _(m) are connected to respective outputterminals of the rows corresponding to the power supply scanning unit50. The signal lines 33 ₁ to 33 _(n) are connected to output terminalsof the columns corresponding to the signal output unit 60.

The write scanning unit 40 is constituted by a shift register circuit,and the like. At the time of writing a signal voltage of a video signalonto each pixel 20 of the pixel array unit 30, the write scanning unit40 performs so-called line sequential scanning in which each of thepixels 20 of the pixel array unit 30 is sequentially scanned in units ofrows by sequentially supplying write scanning signals WS (WS₁ to WS_(m))to the scanning lines 31 (31 ₁ to 31 _(m)).

The power supply scanning unit 50 is constituted by a shift registercircuit and the like, like the write scanning unit 40. The power supplyscanning unit 50 supplies power supply voltages DS (DS₁ to DS_(m)) thatcan switch to a first power supply voltage V_(ccp) and a second powersupply voltage V_(ini) that is lower than the first power supply voltageV_(ccp) to the power supply lines 32 (32 ₁ to 32 _(m)) insynchronization with the line sequential scanning performed by the writescanning unit 40. As will be described later, light emission andnon-light-emission (light-off) of the pixels 20 are controlled as avoltage between the power supply voltages DS V_(ccp) and V_(ini) areswitched.

The signal output unit 60 selectively outputs a signal voltage of avideo signal (which may be described hereinafter simply as a “signalvoltage”) V_(sig) that is based on luminance information supplied from asignal supply source (not shown) and a reference voltage V_(ofs).Herein, the reference voltage V_(ofs) is a voltage serving as areference of the signal voltage of the video signal V_(sig) (forexample, a voltage equivalent to a black level of the video signal), andis used in a threshold value correction process to be described later.

The signal voltage V_(sig) and the reference voltage V_(ofs) output fromthe signal output unit 60 are written into each of the pixels 20 of thepixel array unit 30 via the signal lines 33 (33 ₁ to 33 _(n)) in unitsof pixel rows selected through scanning performed by the write scanningunit 40. In other words, the signal output unit 60 employs a drivingform of line sequential writing in which the signal voltage V_(sig) iswritten in units of rows (lines).

[Pixel Circuit]

FIG. 2 is a circuit diagram showing an example of a detailed circuitconfiguration of a unit pixel (pixel circuit) 20. The light emissionunit of the pixel 20 is constituted by an organic EL element 21 that isan example of a current-driven electro-optical element of which lightemission luminance changes according to a value of a current flowingthrough the device.

As shown in FIG. 2, the pixel 20 includes the organic EL element 21 anda drive circuit that drives the organic EL element 21 by applying acurrent to the organic EL element 21. The cathode electrode of theorganic EL element 21 is connected to a common power supply line 34 thatis commonly wired for all of the pixels 20.

The drive circuit that drives the organic EL element 21 has a 2Tr2Ccircuit configuration including a drive transistor 22, a writingtransistor 23, a retention capacitor 24, and an auxiliary capacitor 25,that is, two transistors (Tr) and two capacitative elements (C). Here,N-channel type thin film transistors (TFTs) are used as the drivetransistor 22 and the writing transistor 23. Here, a conductivecombination of the drive transistor 22 and the writing transistor 23mentioned here is merely an example, but the present disclosure is notlimited to this combination.

One electrode (the source or drain electrode) of the drive transistor 22is connected to the power supply lines 32 (32 ₁ to 32 _(m)) and theother electrode (the source or drain electrode) thereof is connected tothe anode electrode of the organic EL element 21. One electrode (thesource or the drain electrode) of the writing transistor 23 is connectedto each of the signal lines 33 (33 ₁ to 33 _(n)) and the other electrode(the source or the drain electrode) thereof is connected to the gateelectrode of the drive transistor 22. In addition, the gate electrode ofthe writing transistor 23 is connected to the scanning lines 31 (31 ₁ to31 _(m)).

With regard to the drive transistor 22 and the writing transistor 23,one electrode refers to a metal wire electrically connected to onesource or drain region, and the other electrode refers to a metal wireelectrically connected to the other source or drain region. In addition,one electrode may be a source electrode or a drain electrode, and theother electrode may be a drain electrode or a source electrode accordingto the electric potential relation between the one electrode and theother electrode.

One electrode of the retention capacitor 24 is connected to the gateelectrode of the drive transistor 22, and the other electrode thereof isconnected to the other electrode of the drive transistor 22 and to theanode electrode of the organic EL element 21. One electrode of theauxiliary capacitor 25 is connected to the anode electrode of theorganic EL element 21 and the other electrode thereof is connected tothe cathode electrode of the organic EL element 21. That is, theauxiliary capacitor 25 is connected in parallel to the organic ELelement 21.

In the configuration described above, the writing transistor 23 enters aconductive state in which a state of a high voltage applied to the gateelectrode thereof through the scanning line 31 from the write scanningunit 40 becomes an active state in response to the write scanning signalWS. Accordingly, the writing transistor 23 performs sampling on thesignal voltage of the video signal V_(sig) or the reference voltageV_(ofs) according to luminance information supplied from the signaloutput unit 60 through the signal line 33 at different time points andwrites the voltages into the pixel 20. The signal voltage V_(sig) or thereference voltage V_(ofs) written by the writing transistor 23 areretained by the retention capacitor 24.

When the power supply voltage DS of the power supply lines 32 (32 ₁ to32 _(m)) becomes the first power supply voltage V_(ccp), the drivetransistor 22 operates in a saturation region as one electrode thereofserves as the drain electrode and the other electrode serves as thesource electrode. Accordingly, the drive transistor 22 receives supplyof a current from the power supply line 32 and then drives the organicEL element 21 to emit light through current driving. To be morespecific, the drive transistor 22 supplies the driving current of acurrent value according to the voltage value of the signal voltageV_(sig) retained in the retention capacitor 24 to the organic EL element21 to drive the organic EL element 21 to emit light using the current.

When the power supply voltage DS is switched from the first power supplyvoltage V_(ccp) to the second power supply voltage V_(ini), the drivetransistor 22 further operates as a switching transistor as oneelectrode thereof serves as the source electrode and the other electrodethereof serves as the drain electrode. Accordingly, the drive transistor22 stops the supply of the driving current to the organic EL element 21thereby setting the organic EL element 21 to be in a non-light-emissionstate. In other words, the drive transistor 22 also has the function asa transistor which controls light emission and non-light-emission of theorganic EL element 21.

Through the switching operation of the drive transistor 22, it ispossible to set a period in which the organic EL, element 21 is in anon-light-emission state (non-light-emission period) and to control aratio of a light emission period and a non-light-emission period (duty)of the organic EL element 21. With the control of duty, it is possibleto reduce after image and blur caused by light emission of the pixelover one display frame period and particularly to make a level ofquality of a dynamic image more excellent.

Among the first and second power supply voltages V_(ccp) and V_(ini)which are selectively supplied from the power supply scanning unit 50through the power supply line 32, the first power supply voltage V_(ccp)is a power supply voltage for supplying a drive current that drives theorganic EL element 21 to emit light to the drive transistor 22. Inaddition, the second power supply voltage V_(ini) is a power supplyvoltage for applying an inverse bias to the organic EL element 21. Thesecond power supply voltage V_(ini) is set to a voltage lower than thereference voltage V_(ofs), for example, when the threshold voltage ofthe drive transistor 22 is set to V_(th), the second power supplyvoltage is set to a voltage lower than V_(ofs)−V_(th), and preferably toa voltage sufficiently lower than V_(ofs)−V_(th).

Each pixel 20 of the pixel array unit 30 has the function of correctingvariation of a drive current resulting from variation of characteristicsof the drive transistor 22. Here, as the characteristics of the drivetransistor 22, for example, the threshold voltage V_(th) of the drivetransistor 22, and a mobility u of a semiconductor thin filmconstituting a channel of the drive transistor 22 (which will bedescribed hereinafter simply as “mobility u of the drive transistor 22”)are exemplified.

Correction of a variation of a drive current caused due to the variationof the threshold voltage V_(th) (which will be described hereinafter as“threshold correction” in some cases) is performed by initializing agate voltage V_(g) of the drive transistor 22 to the reference voltageV_(ofs). To be specific, an operation of setting an initializationvoltage (reference voltage V_(ofs)) of the gate voltage V_(g) of thedrive transistor 22 as a reference and changing a source voltage V_(s)of the drive transistor 22 toward a potential obtained by reducing thethreshold voltage V_(th) of the drive transistor 22 from theinitialization voltage (reference voltage V_(ofs)) is performed. Whenthis operation progresses, a gate-source voltage V_(gs) of the drivetransistor 22 soon converges on the threshold voltage V_(th) of thedrive transistor 22. A voltage equivalent to the threshold voltageV_(th) is retained in the retention capacitor 24. By retaining thevoltage equivalent to the threshold voltage V_(th) in the retentioncapacitor 24, it is possible to suppress dependency of a drain-sourcecurrent I_(ds) flowing through the drive transistor 22 on the thresholdvoltage V_(th) when the drive transistor 22 is driven at the signalvoltage V_(sig) of a video signal.

Correction of a variation of a drive current caused due to a variationof the mobility u (which will be described hereinafter as “mobilitycorrection”) is performed by flowing a current to the retentioncapacitor 24 via the drive transistor 22 in a state in which the writingtransistor 23 enters a conductive state and the signal voltage V_(sig)of the video signal is written. In other words, the correction isperformed by applying negative feedback to the retention capacitor 24with a feedback amount (correction amount) according to the currentI_(ds) flowing through the drive transistor 22. When a video signal iswritten through the correction of the threshold, the dependency of thedrain-source current I_(ds) on the threshold voltage disappears and thedrain-source current I_(ds) depends on the mobility u of the drivetransistor 22. Accordingly, by applying negative feedback to thedrain-source voltage V_(ds) of the drive transistor 22 with the feedbackamount according to the current I_(ds) flowing through the drivetransistor 22, it is possible to suppress the dependency of thedrain-source current I_(ds) flowing through the drive transistor 22 onthe mobility u.

In the pixel 20 having the foregoing configuration, the auxiliarycapacitor 25 is used to assist the capacitance of the organic EL element21. Accordingly, the auxiliary capacitor 25 is not an essentialconstituent element. That is, the drive circuit of the organic ELelement 21 is not limited to the drive circuit having the 2Tr2c circuitconfiguration of the foregoing configuration. When the capacitance ofthe organic EL element 21 can be sufficiently ensured, a circuitconfiguration of 2Tr1C excluding the auxiliary capacitor 25 can also beemployed. Further, it is possible to use a circuit configuration inwhich a switching transistor is appropriately added as necessary.

[Performance Value (Element Characteristics) Necessary in TFT]

In the organic display device 10 described above, the pixel circuit isconfigured using the plurality of TFTs, that is, the drive transistor 22and the writing transistor 23. Here, the drive transistor 22 is used todirectly drive the organic EL element 21. Accordingly, from theviewpoint of the life span of the organic EL element 21, a currentsupplied from the drive transistor 22 to the organic EL element 21 ispreferably small. In order to suppress the current supplied from thedrive transistor 22 to the organic EL element 21, a TFT that hasrelatively poor (degraded) element characteristics may be used as thedrive transistor 22.

On the other hand, the writing transistor 23 is used for a correctionprocess such as the threshold correction or the mobility correctiondescribed above. Therefore, the writing transistor 23 has to have adrive capability. To compensate for the driving capability, a TFT thathas relatively high element characteristics is preferable as the writingtransistor 23. In this way, even in the TFTs (the drive transistor 22and the writing transistor 23) provided in the same pixel 20,performance values necessary in both of the transistors are notnecessarily the same and there are respective appropriate values.Therefore, it is necessary to separately generate elementcharacteristics between the drive transistor 22 and the writingtransistor 23.

This point is not limited to a case in which a plurality of TFTs areused in the pixel 20 to form a pixel circuit. To be specific, this pointalso applies to a case in which some or all of the peripheral circuitssuch as the write scanning unit 40, the power supply scanning unit 50,and the signal output unit 60 are mounted on the same substrate (thedisplay panel 70) as the pixel array unit 30 constituted such that thepixels 20 are disposed in the matrix form. In this case, the performancevalues necessary in the pixel control TFT (the TFT constituting thepixel circuit) and the peripheral circuit control TFT (the TFTconstituting the peripheral circuit) are not necessarily the same andthere are respective appropriate values. Therefore, it is necessary toseparately generate element characteristics between the pixel controlTFT and the peripheral circuit control TFT.

First Embodiment

An object of a technology of the present disclosure is to separatelygenerate element characteristics of thin film transistors (TFTs)provided on the same substrate without adding a process such as a changein density of ion implantation between the TFTs. In order to achieve theobject, a TFT with a bottom gate structure and a TFT with a top gatestructure on the same substrate are included in a first embodiment ofthe present disclosure. A gate electrode of the TFT with the top gatestructure, that is, a top gate electrode, is provided in the same layeras a wire layer. In other words, the same layer as the wire layer isused as a gate electrode of the TFT with the top gate structure.

Here, the “same layer” means that not only a case of the exact samelayer but also a case of substantially the same layer are included andpresence of various variations occurring in design or manufacturing isallowed. In addition, the “same layer” is assumed to include not only alayer that has the same height and is provided on the same insulationfilm (inter-layer insulation film or an inter-layer film) but also alayer that has a different height and is provided on the same insulationfilm.

In this way, by using the same layer as the wire layer as the gateelectrode (the top gate electrode) of the TFT with the top gatestructure, it is possible to separately generate performance values(element characteristics) necessary in the TFTs in terms of thestructure without employing a method such as a change in density of ionimplantation, that is, without adding a process. Hereinafter, specificexamples of a TFT structure in which a gate electrode of a TFT with atop gate structure is disposed in the same layer as the wire layer and amethod of manufacturing the TFT structure will be described.

In examples to be described below, as shown in FIG. 2, cases in whichpolysilicon is applied to a semiconductor layer in a TFT structure of apixel circuit configured using a plurality of TFTs, that is, the drivetransistor 22 and the writing transistor 23, are employed as examplesfor description. The technology of the present disclosure can also beapplied to a TFT structure in which amorphous silicon ormicrocrystalline silicon, or an oxide semiconductor or an organicsemiconductor, or the like is used in a semiconductor layer.

Example 1

[Structure]

FIG. 3 is a sectional view showing a TFT structure according toExample 1. In FIG. 3, a TFT 80 with a bottom gate structure and a TFT 90with a top gate structure are provided on an insulation transparentsubstrate, for example, a glass substrate 11. In a correspondencerelation with the pixel circuit shown in FIG. 2, the TFT 80 with thebottom gate structure is used as the writing transistor 23 and the TFT90 with the top gate structure is used as the drive transistor 22. Thatis, the drive transistor 22 is constituted by the TFT 90 with the topgate structure and the writing transistor 23 is constituted by TFT 80with the bottom gate structure.

The TFT 80 with the bottom gate structure includes a bottom gateelectrode 81 that is provided on the glass substrate 11, a channelregion 82 that is provided to face the bottom gate electrode 81 with agate insulation film 12 interposed therebetween, and lightly doped drain(LDD) regions 83 _(_1) and 83 _(_2) and source or drain regions 84 _(_1)and 84 _(_2) that are provided on both sides of the channel region 82.An inter-layer insulation film 13 is provided on the channel regions 82,the LDD regions 83 _(_1) and 83 _(_2), and the source or drain regions84 _(_1) and 84 _(_2).

Wires 14 _(_1) and 14 _(_2) are provided on the inter-layer insulationfilm 13. That is, a wire layer is formed on the inter-layer insulationfilm 13. The wires 14 _(_1) and 14 _(_2) are electrically connected tothe source or drain regions 84 _(_1) and 84 _(_2) via contact portions15 _(_1) and 15 _(_2) provided to penetrate through the inter-layerinsulation film 13. That is, portions of the wires 14 _(_1) and 14 _(_2)connected to the contact portions 15 _(_1) and 15 _(_2) serve as sourceor drain electrodes.

The TFT 90 with the top gate structure includes a dummy gate electrode(bottom gate electrode) 91 that is provided on the glass substrate 11and does not have a function of an original gate electrode as in thebottom gate electrode 81. The TFT 90 with the top gate structureincludes not only the dummy gate electrode 91 but also a channel region92 that is provided to face the dummy gate electrode 91 via the gateinsulation film 12 and LDD regions 93 _(_1) and 93 _(_2) and source ordrain regions 94 _(_1) and 94 _(_2) that are provided on both sides ofthe channel region 92.

The TFT 90 with the top gate structure further includes a top gateelectrode 95 that is provided on the inter-layer insulation film 13 toface the channel region 92 and has a function of an original gateelectrode. That is, the gate electrode of the TFT 90 with the top gatestructure, that is, the top gate electrode 95, is provided in the samelayer as the wire layer in which the wires 14 _(_1) and 14 _(_2)including the source or drain electrode of the TFT 80 with the bottomgate structure are formed.

The wires 14 _(_1) and 14 _(_2) and the top gate electrode 95 arecovered with the inter-layer film 16. A pixel electrode 17 is providedon the inter-layer film 16. The pixel electrode 17 is electricallyconnected to the wire 14 _(_2) via a contact portion 18 provided topenetrate through the inter-layer film 16.

FIG. 4 is a plan view showing the TFT structure according to Example 1.FIG. 4 shows only the bottom gate electrode 81, the dummy gate electrode91, the top gate electrode 95, the channel regions 82 and 92, the LDDregions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2), the source or drainregions 84 _(_1), 84 _(_2), 94 _(_1), and 94 _(_2), the contact portions15 _(_1), 15 _(_2), and 15 _(_3), and the wires 14 _(_1), 14 _(_2), and14 _(_3) which are constituent layers of the TFT.

The top gate electrode 95 of the TFT 90 with the top gate structure isintegrated by extending from the wire 14 _(_1) connected (that is,electrically connected) to one source or drain region 84 _(_1) of theTFT 80 with the bottom gate structure via the contact portion 15 _(_1).In addition, the bottom gate electrode 81 of the TFT 80 with the bottomgate structure functions as a gate electrode by supplying a potentialvia the wire 14 _(_3) and the contact portion 15 _(_3). In contrast, thedummy gate electrode 91 of the TFT 90 with the top gate structure is ina floating state without supplying a potential.

[Manufacturing Method]

Next, a method of manufacturing the TFT structure according to Example 1will be described with reference to process diagrams of FIGS. 5A to 5C.

(Process of FIG. 5A)

The bottom gate electrode 81 and the dummy gate electrode 91 are formedby forming a metal film of Mo, W, Al, Ti, Cu, or the like or a metalalloy thin film which becomes the bottom gate electrode 81 on the glasssubstrate 11 so that a thin thickness is about 10 to 500 [nm] accordingto a method such as a sputtering method and performing a patterningprocess.

Next, the gate insulation film 12 is formed by forming a silicon oxidefilm, a silicon nitride film, or a laminated film of a silicon oxidefilm and a silicon nitride film so that a thin thickness is about 20 to500 [nm] according to a method such as a chemical vapor deposition (CVD)method. Thereafter, an amorphous silicon layer is formed on the gateinsulation film 12 so that a film thickness is about 20 to 200 [nm]according to a method such as a CVD method and the amorphous silicon iscrystallized using excimer laser annealing (ELA) or the like.Subsequently, a semiconductor layer which becomes the channel regions 82and 92, for example, a polysilicon layer 61, is formed by performingappropriate impurity implantation. The polysilicon layer 61 may bedirectly formed according to CVD without performing the ELA.

(Process of FIG. 5B)

Next, a photoresist 62 is applied to perform back exposure using thebottom gate electrode 81 and the dummy gate electrode 91 as masks. Thephotoresist 62 may be applied, for example, after about 10 to 200 [nm]of silicon oxide is stacked on the polysilicon layer 61 (not shown).Thereafter, the channel regions 82 and 92 of the TFTs 80 and 90 areformed by performing necessary impurity implantation using the patternedphotoresist 62 as a mask.

(Process of FIG. 5C)

Next, the LDD regions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2) and thesource or drain regions 84 _(_1), 84 _(_2), 94 _(_1), and 94 _(_2) ofthe TFTs 80 and 90 are formed by performing an appropriate lithographyprocess and impurity implantation. Thereafter, the TFT 80 with thebottom gate structure and the TFT 90 with the top gate structure areformed by separating the semiconductor layer through an impurityactivation process and a process of patterning the polysilicon layer 61.

Subsequent processes will be described with reference to FIG. 3. Afterthe TFT 80 with the bottom gate structure and the TFT 90 with the topgate structure are formed, the inter-layer insulation film 13 is formedby forming a silicon oxide film, a silicon nitride film, or a laminatedfilm of a silicon oxide film and a silicon nitride film so that a filmthickness is about 50 to 1500 [nm] according to a method such as a CVDmethod. Subsequently, the contact portions 15 _(_1), 15 _(_2), and 15_(_3) including the contact holes that penetrate through the inter-layerinsulation film 13 are formed through a patterning process. Then, makingcontact to the semiconductor layer (the source or drain regions 84 _(_1)and 84 _(_2)) via the contact portions 15 _(_1) and 15 _(_2) isperformed and making contact to the bottom gate electrode 81 via thecontact portion 15 _(_3) is simultaneously performed (see FIG. 4).

Subsequently, a metal film of Mo, W, Al, Ti, Cu, or the like or an alloyfilm of the metal film of about 100 to 1500 [nm] is formed on theinter-layer insulation film 13 and the contact portions 15 _(_1), 15_(_2), and 15 _(_3) according to a method such as a sputtering method.Thereafter, the wires 14 _(_1) and 14 _(_2) and the top gate electrode95 are integrated through a patterning process. Next, the inter-layerfilm 16 is formed on the inter-layer insulation film 13 using siliconoxide, silicon nitride, or a photosensitive resin such as polyimide sothat a film thickness is about 200 to 3000 [nm] according to a methodsuch as a CVD method or a spin coating method. A laminated film formedof two or more kinds of films may be used in the inter-layer film 16.Next, the contact portion 18 including a contact hole penetratingthrough the inter-layer film 16 is formed through a patterning process.Next, a metal film is formed using a sputtering method or the like andthe pixel electrode 17 is formed through a patterning process.

As described above, the method of manufacturing the TFT structureaccording to Example 1 includes a process forming the bottom gateelectrode 81 and the dummy gate electrode 91, a process of forming thepolysilicon layer 61 which is the semiconductor layer, and the processof forming the gate insulation film 12 between both of the bottom gateelectrode 81 and the dummy gate electrode 91, and the polysilicon layer61. Further, the method includes the process of forming the wire layerincluding the wires 14 _(_1) and 14 _(_2) and the inter-layer insulationfilm 13 on the polysilicon layer 61 and the process of forming theinter-layer film 16 and the pixel electrode 17 on the wire layer. Thetop gate electrode 95 is formed in the same layer as the wire layerincluding the wires 14 _(_1) and 14 _(_2) above the dummy gate electrode91 to which no potential is supplied with the channel region 92interposed therebetween so that the channel region 92 is contained in aplan view.

[Advantageous Effect]

In the TFT structure according to Example 1, since the bottom gatestructure and the top gate structure are used together, the elementcharacteristics are able to be separately generated between the TFTs 80and 90 provided on the same glass substrate 11. In particular, since thetop gate electrode 95 of the TFT 90 is provided in the same layer as thewire layer, the element characteristics are able to be separatelygenerated between the TFTs 80 and 90 without adding a process as in thecase in which the method of changing density of ion implantation isused. In addition, since it is not necessary to add a process, there isan advantage in cost competitiveness, that is, a reduction in cost isachieved.

An example of the element characteristics of the TFT 80 with the bottomgate structure and the TFT 90 with the top gate structure is shown inFIG. 6. For example, when V_(gs) is a gate-source voltage, a currentdifference of about 3.7 multiples of the drive current I_(ds) can beobtained at V_(gs)=15 [V]. This ratio can be obtained as an optimumvalue by appropriately changing processes or design parameters. Theelement characteristics shown in FIG. 6 are merely an example andvarious element characteristics can be obtained by optimizing theprocess.

In addition, the potential of the dummy gate electrode 91 of the TFT 90with the top gate structure may be floating. Moreover, since the topgate electrode 95 is not limited to being disposed on the bottom gateelectrode 81, but may be disposed at any position, there are hardly anyrestrictions imposed on the layout. Further, since the top gateelectrode 95 can be formed using an appropriate inter-layer film as thewire layer including the wires 14 _(_1), 14 _(_2), and 14 _(_3), it ispossible to suppress parasitic capacitance applied to the wire layer.

Here, for example, footprints in a case in which TFTs with the bottomgate structure are used as the drive transistor 22 and the writingtransistor 23 and in a case in which the TFT with the bottom gatestructure and the TFT with the top gate structure are used together asin Example 1 will be examined exemplifying a case in which the circuitof FIG. 2 is applied as the drive circuit of the organic EL element 21.

FIG. 7A is a plan view showing disposition when both of the drivetransistor 22 and the writing transistor 23 are constituted by TFTs withthe bottom gate structure. FIG. 7B is a plan view showing dispositionwhen the drive transistor 22 is constituted by a TFT with the top gatestructure and the writing transistor 23 is constituted by a TFT with thebottom gate structure. Here, the light emission element (21) and thecapacitative elements (24 and 25) are not shown and only the TFTs (22and 23) are shown. In the TFTs (22 and 23), the LDD regions are notshown. In addition, FIGS. 7A and 7B show the contact portions 19 _(_1)and 19 _(_2) in contact with the source and drain regions 94 _(_1) and94 _(_2) of the drive transistor 22 and the wires 14 _(_4) and 14 _(_5)to which the contact portions 19 _(_1) and 19 _(_2) are connected.

In the case of FIG. 7A, a space for contact to a bottom gate electrode91′ (equivalent to the dummy gate electrode 91 in FIG. 3) is essentialin order to replace a potential from one source or drain region 84 _(_1)of the writing transistor 23 (80) to a bottom gate electrode 91′ of thedrive transistor 22 (90′). That is, since both of the transistors areconstituted by the TFTs with the bottom gate structure, as shown in FIG.7A, the wire 14 _(_1) in contact with one source or drain region 84_(_1) of the writing transistor 23 (80) in the contact portion 15 _(_1)necessarily comes into contact with the bottom gate electrode 91′ of thedrive transistor 22 (90′) in a contact portion 19 _(_0).

In contrast, in the case of FIG. 7B, that is, in the case of the TFTstructure according to Example 1, since the wire 14 _(_1) of which apotential is replaced from one source or drain region 84 _(_1) of thewriting transistor 23 (80) extends and is used as the top gate electrode95 of the drive transistor 22 (90), the footprint can be reduced morethan in the case of FIG. 7A in FIG. 2, the drive transistor 22constituted by the TFT 90 with the top gate structure is a TFT thatcontrols a current flowing through the organic EL element 21. Here, fromthe viewpoint of the life span of the organic EL element 21, it isnecessary to reduce a drive current of the drive transistor 22. In theTFT structure according to Example 1, as shown in FIG. 6, the currentdrive capability of the TFT 90 with the top gate structure can besuppressed to be low. Therefore, it is possible to provide the TFTstructure appropriate for the drive element of the organic EL element21.

Example 2

Example 2 is a modification example of Example 1. FIG. 8A is a plan viewshowing a TFT structure according to Example 2. Portions from the bottomgate electrode 81 and the dummy gate electrode 91 to the pixel electrode17 are formed through the same processes as those of Example 1. The TFTstructure according to Example 2 is different from the TFT structureaccording to Example 1 in that the source or drain region 84 _(_1) ofthe TFT 80 with the bottom gate structure and the source or drain region94 _(_2) of the TFT 90 with the top gate structure are directlyconnected in a plan view without passing through the wire layerincluding the wires 14 _(_4) and 14 _(_5). That is, the TFTs 80 and 90are connected in series to function as one TFT 101. The bottom gateelectrode 81 of the TFT 80 and the top gate electrode 95 of the TFT 90may have the same potential.

For example, in a process and element design realizing the elementcharacteristics of FIG. 6, a threshold voltage of current design of theTFT 90 with the top gate structure is higher than a threshold voltage ofthe TFT 80 with the bottom gate structure. As described above, in theTFT structure according to Example 2, the TFT 101 is constituted suchthat the TFT 80 with the bottom gate structure and the TFT 90 with thetop gate structure are connected in series. Therefore, when the bottomgate electrode 81 and the top gate electrode 95 have the same potential,a threshold voltage of the TFT 101 is identical to a threshold voltageof the TFT 90 with the top gate structure. On the other hand, a currentdrive capability of the TFT 101 is less than a current drive capabilityof the TFT 90 with the top gate structure.

Accordingly, in the TFT structure according to Example 2, the elementcharacteristics are able to be separately generated between the TFT 101having element characteristics different from those of any of the TFT 80with the bottom gate structure and the TFT 90 with the top gatestructure without adding a process as in a case in which a method ofchanging density of ion implantation is used. The elementcharacteristics in the TFT structure according to Example 2 satisfy thefollowing magnitude relations:threshold voltages: TFT80<TFT90=TFT101; andcurrent drive capability: TFT80>TFT90>TFT101.

Example 3

Example 3 is a modification example of Example 1. FIG. 8B is a plan viewshowing a TFT structure according to Example 3. Portions from the bottomgate electrode 81 and the dummy gate electrode 91 to the pixel electrode17 are formed through the same processes as those of Example 1. UnlikeExample 2, the source or drain regions 84 _(_1) and 84 _(_2) of the TFT80 with the bottom gate structure and the source or drain region 94_(_1) and 94 _(_2) of the TFT 90 with the top gate structure aredirectly connected in a plan view without passing through the wire layerincluding the wires 14 _(_4) and 14 _(_5). That is, the TFTs 80 and 90are connected in parallel to functions as one TFT 102. The bottom gateelectrode 81 of the TFT 80 and the top gate electrode 95 of the TFT 90may have the same potential.

As described above, in the TFT structure according to Example 2, the TFT102 is constituted such that the TFT 80 with the bottom gate structureand the TFT 90 with the top gate structure are connected in parallel.Therefore, when the bottom gate electrode 81 and the top gate electrode95 have the same potential, a threshold voltage of the TFT 102 isidentical to a threshold voltage of the TFT 80 with the bottom gatestructure. On the other hand, a current drive capability of the TFT 102is greater than a current drive capability of the TFT 80 with the bottomgate structure.

Accordingly, in the TFT structure according to Example 3, the elementcharacteristics are able to be separately generated between the TFT 102having element characteristics different from those of any of the TFT 80with the bottom gate structure and the TFT 90 with the top gatestructure without adding a process as in the case in which the method ofchanging density of ion implantation is used. The elementcharacteristics in the TFT structure according to Example 3 satisfy thefollowing magnitude relations:threshold voltages: TFT102=TFT80<TFT90; andcurrent drive capability: TFT102>TFT80>TFT90.

Example 4

[Structure]

FIG. 9 is a sectional view showing a TFT structure according to Example4. While the wire layer and the inter-layer film have a one-layerstructure in Example 1, the wire layer and the inter-layer film have atwo-layer structure in Example 4. Further, a TFT structure according toExample 4 is different from the TFT structure according to Example 1 inan element structure of the TFT 90 with the top gate structure. Anelement structure of the TFT 80 with the bottom gate structure is thesame as the TFT structure according to Example 1.

In Example 4, in the correspondence relation with the pixel circuitshown in FIG. 2, the TFT 80 with the bottom gate structure is used asthe writing transistor 23 and the TFT 90 with the top gate structure isused as the drive transistor 22 as in Example 1. That is, the drivetransistor 22 is constituted by the TFT 90 with the top gate structureand the writing transistor 23 is constituted by the TFT 80 with thebottom gate structure.

As shown in FIG. 9, the wires 14 _(_1) and 14 _(_2) are provided on theinter-layer insulation film 13 as wires of a first layer. The wires 14_(_1) and 14 _(_2) are in contact with (electrically connected to) thesource or drain regions 84 _(_1) and 84 _(_2) through the contactportions 15 _(_1) and 15 _(_2). In addition, a contact hole 15B isformed in a site of the inter-layer insulation film 13 corresponding tothe channel region 92 and the LDD regions 93 _(_1) and 93 _(_2) of theTFT 90. A gate insulation film 52 is provided on the inter-layerinsulation film 13, on the wires 14 _(_1) and 14 _(_2), and in thecontact hole 15B, and the first inter-layer film 16 is provided on thegate insulation film 52.

Wires 51 _(_1) and 51 _(_2) are provided as a second wire layer on thefirst inter-layer film 16. The wire 51 _(_1) is in contact with, thatis, is electrically connected to, the wire 14 _(_1) through the contactportion 54 _(_1) and the contact hole 52A of the gate insulation film52. A contact hole 16B is formed in a site of the first inter-layer film16 corresponding to the TFT 90 with the top gate structure. The top gateelectrode 95 of the TFT 90 with the top gate structure is provided inthe same layer as the second wire layer including the wires 51 _(_1) and51 _(_2) on the first inter-layer film 16, in the contact hole 16B, andon the gate insulation film 52. The wires 51 _(_1) and 51 _(_2) and thetop gate electrode 95 are covered with the second inter-layer film 53.

FIG. 10 is a plan view showing a TFT structure according to Example 4.FIG. 10 shows only the bottom gate electrode 81, the dummy gateelectrode 91, the top gate electrode 95, the channel regions 82 and 92,the LDD regions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2), the sourceor drain regions 84 _(_1), 84 _(_2), 94 _(_1), and 94 _(_2), the contactportions 15 _(_1), 15 _(_2), 15 _(_3), and 54 _(_1), the wires 14 _(_1),14 _(_2), and 14 _(_3), and the wire 51 _(_1) which are constituentlayers of the TFT.

The top gate electrode 95 is integrated by extending the wire 51 _(_1)connected via the contact portion 54 _(_1) and the contact hole 52A ofthe gate insulation film 52 from the wire 14 _(_1) connected to onesource or drain region 84 _(_1) of the TFT 80 with the bottom gatestructure via the contact portion 15 _(_1). In addition, the bottom gateelectrode 81 functions as a gate electrode by supplying a potential viathe wire 14 _(_3) and the contact portion 15 _(_3). The dummy gateelectrode 91 is in a floating state without supplying a potential.

[Manufacturing Method]

Next, a method of manufacturing the TIFF structure according to Example4 will be described with reference to process diagrams of FIGS. 11A and11B.

(Process of FIG. 11A)

A process of FIG. 11A corresponds to the process of FIG. 5C. That is,the TFT 80 with the bottom gate structure and the TFT 90 with the topgate structure are formed through the processes of FIGS. 5A to 5C.Thereafter, an inter-layer insulation film 13 is formed by forming asilicon oxide film, a silicon nitride film, or a laminated film of asilicon oxide film and a silicon nitride film according to a method suchas a CVD method. Thereafter, a contact hole 15A penetrating through theinter-layer insulation film 13 is formed through a patterning process.However, a contact hole 15B penetrating through the inter-layerinsulation film 13 is simultaneously formed so that the channel region92 of the TFT 90 with the top gate structure is contained unlike Example1.

(Process of FIG. 11B)

Subsequently, as in Example 1, making contact to the semiconductor layer(the source or drain regions 84 _(_1) and 84 _(_2)) via the contactportions 15 _(_1) and 15 _(_2) including the contact hole 15A isperformed and contact to the bottom gate electrode 81 in the contactportion 15 _(_3) is also simultaneously performed (see FIG. 10). Next, afirst metal film is formed on the inter-layer insulation film 13, in thecontact hole 15A, and in the contact hole 15B according to a method suchas a sputtering method. Thereafter, a first wire layer including thewires 14 _(_1) and 14 _(_2) is formed by patterning the first metal filmin the contact hole 15B so that the first metal film is removed.

Thereafter, the gate insulation film 52 constituted by a high dielectricinter-layer film using silicon oxide, silicon nitride, or a highdielectric material such as hafnium oxide or hafnium silicate is formedaccording to a method such as a CVD method or a sputtering method sothat a film thickness is about 10 to 500 [nm]. Next, a process of apatterning process is performed to form the contact hole 52A penetratingthe gate insulation film 52 (the high dielectric inter-layer film).

Subsequent processes will be described with reference to FIG. 9. Afterthe contact hole 52A is formed, the first inter-layer film 16 is formedon the gate insulation film 52 using silicon oxide, silicon nitride, ora photosensitive resin such as polyimide according to a method such as aCVD method or a spin coating method so that a film thickness is about200 to 3000 [nm]. Thereafter, the contract holes 16A and 16B penetratingthe inter-layer film 16 are formed through a patterning process. Thecontract hole 16A is formed to overlap the contact hole 52A penetratingthrough the gate insulation film 52 in a plan view (in FIG. 9, acontaining state is indicated). The contact hole 16B is formed so thatthe contact hole 15B penetrating the inter-layer insulation film 13 iscontained in a plan view.

Next, a second metal film of Mo, W, Al, Ti, Cu, or the like or an alloyfilm of the metal film is formed according to a method such as asputtering method so that a film thickness is about 100 to 150 [nm].Thereafter, the wires 51 _(_1) and 51 _(_2) and the top gate electrode95 are integrated as a second wire layer through a patterning process.Accordingly, the top gate electrode 95 is disposed to face the channelregion 92 with the gate insulation film 52 constituted by a highdielectric inter-layer film therebetween.

Next, the second inter-layer film 53 is formed on the first inter-layerfilm 16 using silicon oxide, silicon nitride, or a photosensitive resinsuch as polyimide so that a film thickness is about 200 to 3000 [nm]according to a method such as a CVD method or a spin coating method.Thereafter, the contract portion 18 including the contact holepenetrating the second inter-layer film 53 is formed through apatterning process. Next, a metal film is formed using a sputteringmethod or the like to form the pixel electrode 17 through a patterningprocess.

As described above, the method of manufacturing the TFT structureaccording to Example 4 includes the process of forming the bottom gateelectrode 81 and the dummy gate electrode 91, the process of forming thepolysilicon layer 61 which is the semiconductor layer, the process offorming the gate insulation film 12 between both of the bottom gateelectrode 81 and the dummy gate electrode 91, and the polysilicon layer61, and the process of forming the first wire layer including the wires14 _(_1) and 14 _(_2) and the inter-layer insulation film 13 on thepolysilicon layer 61. Further, the method includes the process offorming the contact hole (opening hole) 15B in the inter-layerinsulation film 13 and forming the first inter-layer film 16 and thesecond wire layer including the wires 51 _(_1) and 51 _(_2) on the firstwire layer and the process of forming the second inter-layer film 53 andthe pixel electrode 17 on the second wire layer. The contact hole 15B isopened so that the channel region 92 above the dummy gate electrode 91to which no potential is supplied is contained in a plan view, and thetop gate electrode 95 is formed in the same layer as the second wirelayer in the contact hole 15B.

[Advantageous Effect]

In the TFT structure according to Example 4, as in the TFT structureaccording to Example 1, the element characteristics are able to beseparately generated between the TFT 80 with the bottom gate structureand the TFT 90 with the top gate structure without adding a process asin the case in which the method of changing density of ion implantationis used. In addition, Between the TFT 90 with the top gate structure andthe TFT structure according to Example 1, the shape, the material, andthe like of the top gate electrode 95 are different and a different gateinsulation film 52 is interposed between the channel region 92 and thetop gate electrode 95. Therefore, it is possible to obtain differentelement characteristics from the TFT 90 according to Example 1. Further,when the film thickness or a film kind of the gate insulation film 52 isselected, it is possible to reduce an influence of the first layerincluding the wires 14 _(_1) and 14 _(_2) on parasitic capacitancefurther than the TFT90 according to Example 1. Therefore, there is theadvantage that the degree of freedom of selection is improved.

Example 5

Example 5 is a modification example of Example 4. FIG. 12A is a planview showing a TFT structure according to Example 5. Portions from thebottom gate electrode 81 and the dummy gate electrode 91 to the pixelelectrode 17 are formed through the same processes as those of Example4. The TFT structure according to Example 5 is different from the TFTstructure according to Example 4 in that the source or drain region 84_(_1) of the TFT 80 and the source or drain region 94 _(_2) of the TFT90 are directly connected in a plan view without passing through thefirst wire layer including the wires 14 _(_4) and 14 _(_5) and thesecond wire layer including the wires 51 _(_4) and 51 _(_5). That is,the TFTs 80 and 90 are connected in series to functions as one TFT 103.The bottom gate electrode 81 of the TFT 80 and the top gate electrode 95of the TFT 90 may have the same potential.

In this way, the TFT structure according to Example 5 is constitutedsuch that the TFT 103 is connected in series to the TFT 80 with thebottom gate structure and the TFT 90 with the top gate structure.Accordingly, when the bottom gate electrode 81 and the top gateelectrode 95 have the same potential, a threshold voltage of currentdefinition of the TFT 101 can be the same value as a higher thresholdvoltage between the threshold voltages of the TFTs 80 and 90, as in theTFT structure according to Example 2. In addition, the current drivecapability of the TFT 101 can be set to a value less than a lowercurrent drive capability between the current drive capabilities of theTFTs 80 and 90.

Accordingly, in the TFT structure according to Example 5, the elementcharacteristics are able to be separately generated in the TFT 103having element characteristics different from those of any of the TFT 80with the bottom gate structure and the TFT 90 with the top gatestructure without adding a process as in the case in which the method ofchanging density of ion implantation is used.

Example 6

Example 6 is a modification example of Example 4. FIG. 12B is a planview showing a TFT structure according to Example 6. Portions from thebottom gate electrode 81 and the dummy gate electrode 91 to the pixelelectrode 17 are formed through the same processes as those of Example4. Unlike Example 4, the source or drain regions 84 _(_1) and 84 _(_2)of the TFT 80 and the source or drain regions 94 _(_1) and 94 _(_2) ofthe TFT 90 are directly connected in a plan view without passing throughthe first wire layer including the wires 14 _(_4) and 14 _(_5) and thesecond wire layer including the wires 51 _(_4) and 51 _(_5). That is,the TFTs 80 and 90 are connected in parallel to function as one TFT 104.The bottom gate electrode 81 of the TFT 80 and the top gate electrode 95of the TFT 90 may have the same potential.

In this way, the TFT structure according to Example 6 is constitutedsuch that the TFT 104 is connected in parallel to the TFT 80 with thebottom gate structure and the TFT 90 with the top gate structure.Accordingly, when the bottom gate electrode 81 and the top gateelectrode 95 have the same potential, a threshold voltage of currentdefinition of the TFT 101 can be the same value as a lower thresholdvoltage between the threshold voltages the TFTs 80 and 90, as in the TFTstructure according to Example 3. In addition, the current drivecapability of the TFT 101 can be set to a value greater than a highercurrent drive capability between the current drive capabilities of theTFTs 80 and 90.

Accordingly, in the TFT structure according to Example 6, the elementcharacteristics are able to be separately generated in the TFT 104having element characteristics different from those of any of the TFT 80with the bottom gate structure and the TFT 90 with the top gatestructure without adding a process as in the case in which the method ofchanging density of ion implantation is used.

Description of Second Embodiment

In an active matrix display device such as a liquid crystal displaydevice or an organic EL display device, a variation of elementcharacteristics occurs in a transistor driving a light emission unit anda transistor constituting a peripheral circuit in some cases. Therefore,repairing is performed to restore pixels including transistors which donot satisfy desired characteristics (have characteristics worse thanpredetermined characteristics) by performing a so-called array test in astep of forming transistors and determining (ascertaining) elementcharacteristics (pixel characteristics) of individual transistors.

In a second embodiment, in a display device in which thin filmtransistors (TFTs), particularly, TFTs with a bottom gate structure, areused as transistors driving light emission units and transistorsconstituting a peripheral circuit, an array test is assumed to beperformed to ascertain the element characteristics of the individualTFTs in a step of forming the TFTs. With regard to the TFTs with thebottom gate structure of which element characteristics are determinednot to satisfy desired characteristics, the pixels including the TFTsare rescued (repaired) in the array test by adding top gate electrodesto the TFTs with the bottom gate structure since sufficient elementcharacteristics may not be obtained only with the bottom gate structure.The addition of the top gate electrodes to the TFTs with the bottom gatestructure can be realized using, for example, a technology (a so-calledwiring CVD method) for performing wiring when a metal thin film isformed according to a CVD method.

Hereinafter, specific examples in which a top gate electrode is added toa TFT with the bottom gate structure of which element characteristicsare determined not to satisfy desired characteristics in the array testwill be described.

Example 7

In Example 7, in a TFT structure in which there is only the TFT 80 withthe bottom gate structure in the TFT structure according to Example 1and there is no TFT 90 with the top gate structure, pixels including theTFTs 80 which do not satisfy desired characteristics are repaired.

[Structure]

FIG. 13A is a sectional view showing a TFT structure according toExample 7. FIG. 13A shows a TFT structure in which a top gate electrode85 indicated by a dotted line is added to the TFT 80 with the bottomgate structure.

In Example 7, the TFT 80 which does not satisfy desired characteristicsis specified by performing the array test for determining the pixelcharacteristics in a step of forming portions from the bottom gateelectrode 81 to the wire layer including the wires 14 _(_1) and 14 _(_2)in the TFT 80 with the bottom gate structure. In the array test, forexample, the TFT 80 with the bottom gate structure in which a currentdrive capability is less than a predetermined value is specified as arepairing target TFT. The top gate electrode 85 is added to therepairing target TFT 80 which is determined not to satisfy the desiredcharacteristics in the array test.

The top gate electrode 85 is provided to face the bottom gate electrode81 of the repairing target TFT 80 with the channel region 82 interposedtherebetween. The addition of the top gate electrode 85 can be realizedby forming a metal film of W or the like only in a site above thechannel region 82 of the TFT 80 according to a laser CVD method or usinga gold paste or the like.

In the TFT structure of FIG. 13A, a TFT 80A with the bottom gatestructure is constituted by the bottom gate electrode 81, the channelregion 82, the LDD regions 83 _(_1) and 83 _(_2), and the source ordrain regions 84 _(_1) and 84 _(_2). In addition, a TFT 80B with the topgate structure is constituted by the channel region 82, the LDD regions83 _(_1) and 83 _(_2), the source or drain regions 84 _(_1) and 84_(_2), and the top gate electrode 85.

FIG. 13B is a plan view showing a TFT structure according to Example 7.FIG. 13B shows only the bottom gate electrode 81, the channel region 82,the LDD regions 83 _(_1) and 83 _(_2), the source or drain regions 84_(_1) and 84 _(_2), the top gate electrode 85, the contact portions 15_(_1), 15 _(_2), and 15 _(_3), and the wires 14 _(_1), 14 _(_2), and 14_(_3) which are constituent layers of the TFT.

The top gate electrode 85 of the TFT 80B is provided to be electricallyconnected to the wire 14 _(_3) connected to the bottom gate electrode 81of the TFT 80A in the contact portion 15 _(_3). Accordingly, the TFT 80Awith the bottom gate structure and the TFT 80B with the top gatestructure which are located above and below each other with the channelregion 82 interposed therebetween function as the TFT 105 with alaminated structure in which the bottom gate structure and the top gatestructure are laminated, in other words, function as the TFT 105 with abottom/top both-sided gate structure.

[Manufacturing Method]

Portions from the bottom gate electrode 81 to the wire layer includingthe wires 14 _(_1) and 14 _(_2) are formed through the same processes asthose of Example 1. In this step, the TFT 80A with the bottom gatestructure is formed. When the wire layer including the wires 14 _(_1)and 14 _(_2) is formed, the top gate electrode 85 is not yet formed.

In a step of forming the TFT 80A with the bottom gate structure, thearray test for determining the pixel characteristics is performed tospecify the TFT 80A which does not satisfy the desired characteristics,for example, the TFT 80A with the bottom gate structure of which thecurrent drive capability is less than the predetermined value.Subsequently, a metal film of W or the like is formed only in a siteabove the channel region 82 of the TFT 80A according to a laser CVDmethod or using a gold paste or the like to form the top gate electrode85 so that a film thickness is about 50 to 500 [nm]. At this time, thetop gate electrode 85 is formed so that the channel region 82 iscontained in a plan view. Accordingly, the top gate electrode 85functions as the top gate electrode of the TFT 80B. After the top gateelectrode 85 is formed, portions from the inter-layer film 16 to thepixel electrode 17 are formed through the same processes as those ofExample 1.

As described above, the method of manufacturing the TFT structureaccording to Example 7 includes the process of forming the bottom gateelectrode 81, the process of forming the polysilicon layer 61, theprocess of forming the gate insulation film 12 between both of thebottom gate electrode 81 and the polysilicon layer 61, and the processof forming the wire layer including the wires 14 _(_1) and 14 _(_2) andthe inter-layer insulation film 13 on the polysilicon layer 61. Themethod further includes the process of performing the array test and thewiring and the process of forming the inter-layer film 16 and the pixelelectrode 17 on the wire layer including the wires 14 _(_1) and 14_(_2). The top gate electrode 85 is formed in the same layer as the wirelayer including the wires 14 _(_1) and 14 _(_2) above the bottom gateelectrode 81 with the channel region 82 interposed therebetween so thatthe channel region 82 is contained in a plan view

[Advantageous Effect]

As described above, the top gate electrode 85 is added in the same layeras the wire layer including the wires 14 _(_1) and 14 _(_2) to therepairing target TFT 80A of which the current drive capability is lessthan the predetermined value and which is determined not to satisfy thedesired characteristics according to, for example, the laser CVD methodin the array test. Accordingly, since the TFT 105 according to Example 7has the laminated structure (bottom/top both-sided gate structure) ofthe TFT 80A with the bottom gate structure and the TFT 80B with the topgate structure, it is possible to improve the current drive capabilitymore than in the TFT 80A with only the bottom gate structure. Byimproving the current drive capability, it is possible to correct thecharacteristics of the TFT 80A with the original bottom gate structureof which sufficient element characteristics are unobtainable in only thebottom gate structure. That is, it is possible to repair the pixel thatincludes the TFT 80A with the bottom gate structure which does notsatisfy the desired characteristics.

Example 8

In Example 8, not only the TFT 80 with the bottom gate structure butalso the dummy gate electrode 91 are included in the TFT structureaccording to Example 1, but it is assumed that a TFT with a structurewhich does not include the top gate electrode 95 is included as aredundant TFT 90A (see FIG. 14A). When the TFT 80 with the bottom gatestructure has a critical defect such as leakage between a source and adrain and a pixel including the TFT 80 becomes, for example, a defectpixel such as a bright spot, the repairing target TFT 80 having thedefect is broken. A top gate electrode is added to the redundant TFT 90Awhich is another TFT provided on the same glass substrate 11 as therepairing target TFT 80. The redundant TFT 90A with the top gatestructure is used instead of the TFT 80. In this case, as in Example 3shown in FIG. 8B, it is assumed that the redundant TFT 90A is connectedin parallel to the repairing target TFT 80 with the bottom gatestructure.

[Structure]

FIG. 14A is a sectional view showing a TFT structure according toExample 8. The TFT structure according to Example 8 includes theredundant TFT 90A and the TFT 80 with the bottom gate structure. When itis determined that the TFT 80 with the bottom gate structure has acritical defect such as leakage between a source and a drain in an arraytest for determining pixel characteristics, the redundant TFT 90A has afunction of a TFT with the top gate structure by including the top gateelectrode 95 added later and indicated by a dotted line in FIG. 14A.

FIG. 14B is a plan view showing a TFT structure according to Example 8.FIG. 14B shows only the bottom gate electrode 81, the dummy gateelectrode 91, the top gate electrode 95, the channel regions 82 and 92,the regions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2), the source ordrain regions 84 _(_1), 84 _(_2), 94 _(_1), and 94 _(_2), the contactportions 15 _(_1), 15 _(_2), and 15 _(_3), and the wires 14 _(_4), 14_(_2), and 14 _(_3) which are constituent layers of the TFT.

A disconnection process is performed using a laser repairing technologyon the TFT 80 with the bottom gate structure determined to have acritical defect such as leakage between a source and a drain in an arraytest. A laser repair site of disconnection from the TFT 80 is indicatedby a dotted line X in FIG. 14B. The laser repairing disconnection may beperformed on the source or drain region 84 _(_1) or 84 _(_2) of the TFT80, the bottom gate electrode 81, or the wire 14 _(_3) connected to thebottom gate electrode 81 in the contact portion 15 _(_3).

The top gate electrode 95 is connected to the wire 14 _(_4) supplying agate voltage of the redundant TFT 90A and the gate electrode 91 is adummy gate electrode. Accordingly, the redundant TFT 90A functions as aTFT with the top gate structure. The top gate electrode 95 may have thesame potential as the bottom gate electrode 81. The TFT 80 with thebottom gate structure and the redundant TFT 90A are connected inparallel. Accordingly, the characteristics of the TFT 106 (with the TFTstructure according to Example 8) after the laser repairingdisconnection from the TFT 80 and the formation of the top gateelectrode 95 of the redundant TFT 90A are identical to thecharacteristics of the redundant TFT 90A with the top gate structure.

[Manufacturing Method]

Portions from the bottom gate electrode 81 and the dummy gate electrode91 to the wire layer including the wires 14 _(_1) and 14 _(_2) areformed through the same processes as those of Example 1. The TFT 80 hasthe bottom gate structure and the redundant TFT 90A has the top gatestructure, but the top gate electrode 95 of the redundant TFT 90A is notformed when the wire layer including the wires 14 _(_1) and 14 _(_2) isformed unlike Example 1.

In a step of forming the wire layer including the wires 14 _(_1) and 14_(_2), an array test for determining the pixel characteristics isperformed to specify the TFT 80 which does not satisfy the desiredcharacteristics. In this example, the TFT 80 having a critical defectsuch as leakage between a source and a drain is specified as the TFTwhich does not satisfy the desired characteristics. The TFT 80 specifiedas the TFT which does not satisfy the desired characteristics isdisconnected using laser repairing.

Next, a metal film of W or the like is formed only in a site in whichthe top gate electrode 95 of the redundant TFT 90A is disposed accordingto a laser CVD method or using a gold paste or the like to form the topgate electrode 95 so that a film thickness is about 50 to 500 [nm]. Atthis time, the top gate electrode 95 is formed so that the channelregion 92 is contained in a plan view. Accordingly, the top gateelectrode 95 to be added subsequently functions as the top gateelectrode of the redundant TFT 90A. After the top gate electrode 95 isformed, portions from the inter-layer film 16 to the pixel electrode 17are formed through the same processes as those of Example 1.

As described above, as in Example 1, the method of manufacturing the TFTstructure according to Example 8 includes the process of forming thebottom gate electrode 81, the process of forming the polysilicon layer61, the process of forming the gate insulation film 12 between both ofthe bottom gate electrode 81 and the polysilicon layer 61, and theprocess of forming the wire layer including the wires 14 _(_1) and 14_(_2) and the inter-layer insulation film 13 on the polysilicon layer61. The method further includes the process of performing the array testand the wiring and the process of forming the inter-layer film 16 andthe pixel electrode 17 on the wire layer including the wires 14 _(_1)and 14 _(_2). Above the dummy gate electrode 91 to which no potential issupplied in a layer below the channel region 92 connected to the sourceor drain region 84 _(_2) of the TFT 80 disconnected in the laserrepairing process, the top gate electrode 95 is formed in the same layeras the wire layer including the wires 14 _(_1) and 14 _(_2) with thechannel region 92 interposed therebetween so that the channel region 92is contained in a plan view.

[Advantageous Effect]

In the TFT structure according to Example 8, after pixel darkening isperformed once by fracturing the TFT 80 with the bottom gate structuredetermined to have a critical defect such as a leakage between a sourceand a drain, the top gate electrode 95 is added to the redundant TFT 90Ain the same layer as the wire layer including the wires 14 _(_1) and 14_(_2). Accordingly, in order to cause the redundant TFT 90A to functionas the TFT with the top gate structure, a pixel with a bright spotdefect caused in the TFT 80 with the bottom gate structure having acritical defect such as leakage between a source and a drain can berescued (repaired).

Example 9

Example 9 is a modification example of Example 7. The technologyaccording to Example 7 is applied to a TFT structure which is atwo-layer structure of a wire layer and an inter-layer film.

[Structure]

FIG. 15A is a sectional view showing a TFT structure according toExample 9. FIG. 15A shows a TFT structure after the top gate electrode85 indicated by a dotted line and having a different shape or the likefrom Example 7 is added to the TFT 80 with the bottom gate structure.

In the TFT structure according to Example 9, the TFT 80 with the bottomgate structure has basically the same structure as the TFT 90 of the TFTstructure according to Example 4 shown in FIG. 9. Here, as in Example 7,the top gate electrode 85 is added later to the TFT 80 with the bottomgate structure determined not to satisfy the desired characteristics inan array test.

In the TFT structure of FIG. 15A, the TFT 80A with the bottom gatestructure is constituted by the bottom gate electrode 81, the channelregion 82, the LDD regions 83 _(_1) and 83 _(_2), and the source ordrain regions 84 _(_1) and 84 _(_2). In addition, the TFT 80B with thetop gate structure is constituted by the channel region 82, the LDDregions 83 _(_1) and 83 _(_2), the source or drain regions 84 _(_1) and84 _(_2), and the top gate electrode 85.

FIG. 15B is a plan view showing a TFT structure according to Example 9.FIG. 15B shows only the bottom gate electrode 81, the top gate electrode85, the channel region 82, the LDD regions 83 _(_1) and 83 _(_2), thesource or drain regions 84 _(_1) and 84 _(_2), the contact holes 15B and16B, the contact portions 15 _(_3) and 54 _(_1), and the wires 14 _(_1)and 51 _(_1) which are constituent layers of the TFT.

The top gate electrode 85 of the TFT 80B is provided to be electricallyconnected to the wire 14 _(_1) connected to the bottom gate electrode 81of the TFT 80A via the contact portion 15 _(_3). To be specific, the topgate electrode 85 is electrically connected to the wire 51 _(_1)connected to the wire 14 _(_1) via the contact portion 54 _(_1).Accordingly, the TFT 80A with the bottom gate structure and the TFT 80Bwith the top gate structure which are located above and below each otherwith the channel region 82 interposed therebetween function as a TFT 107with a laminated structure in which both of the TFTs 80A and 80B arelaminated, in other words, the TFT 107 with a bottom/top both-sided gatestructure.

[Manufacturing Method]

Portions from the bottom gate electrode 81 to the wire layer includingthe wires 51 _(_1) and 51 _(_2) are formed through the same processes asthose of Example 1. The TFT 80A has the bottom gate structure. UnlikeExample 4, the top gate electrode 85 is not formed when the wire layerincluding the wires 51 _(_1) and 51 _(_2) is formed.

In a step of forming the TFT 80A with the bottom gate structure, thearray test for determining the pixel characteristics is performed tospecify the TFT 80A which does not satisfy the desired characteristics,for example, the TFT 80A with the bottom gate structure of which thecurrent drive capability is less than the predetermined value.Subsequently, a metal film of W or the like is formed only in a siteabove the channel region 82 of the TFT 80A according to a laser CVDmethod or using a gold paste or the like to form the top gate electrode85 so that a film thickness is about 50 to 500 [nm]. At this time, thetop gate electrode 85 is formed so that the channel region 82 iscontained in a plan view. Accordingly, the top gate electrode 85functions as a gate electrode of the TFT 80B with the top gatestructure. After the top gate electrode 85 is formed, portions from theinter-layer film 53 to the pixel electrode 17 are formed through thesame processes as those of Example 4.

As described above, as in Example 4, the method of manufacturing the TFTstructure according to Example 9 includes the process of forming thebottom gate electrode 81, the process of forming the polysilicon layer61 which is the semiconductor layer, the process of forming the gateinsulation film 12 between both of the bottom gate electrode 81 and thepolysilicon layer 61, and the process of forming the wire layerincluding the wires 14 _(_1) and 14 _(_2) and the inter-layer insulationfilm 13 on the polysilicon layer 61. Further, the method includes theprocess of forming the contact hole (opening hole) 15B in theinter-layer insulation film 13, the process of forming the firstinter-layer film 16 and the second wire layer including the wires 51_(_1) and 51 _(_2) on the first wire layer, and the process of formingthe second inter-layer film 53 and the pixel electrode 17 on the secondwire layer. The contact hole 15B is opened so that the channel region 82above the bottom gate electrode 81 is contained in a plan view, and thetop gate electrode 85 is formed in the same layer as the second wirelayer in the contact hole 15B.

[Advantageous Effect]

In the TFT structure according to Example 9, for example, the top gateelectrode 85 is added in the same layer as the second wire layerincluding the wires 51 _(_1) and 51 _(_2) according to, for example, alaser CVD method to the TFT 80A with the bottom gate structure of whichthe current drive capability is less than the predetermined value andwhich is determined not to satisfy the desired characteristics in thearray test. Accordingly, since the TFT 80A with the bottom gatestructure and the TFT 80B with the top gate structure function as theTFT 107 with the laminated structure of the TFTs 80A and 80B, thecurrent drive capability can be improved more than in the TFT 80A withonly the bottom gate structure. By improving the current drivecapability, it is possible to correct the characteristics of the TFT 80Awith the original bottom gate structure of which sufficient elementcharacteristics are unobtainable in only the bottom gate structure. Inaddition, the TFT 80B with the top gate structure has a different shape,material or the like of the top gate electrode 85 from the TFT 80Baccording to Example 7. Further, since a different gate insulation film52 is interposed between the channel region 82 and the top gateelectrode 85, it is possible to obtain different element characteristicsfrom the TFT 80B according to Example 7.

Example 10

Example 10 is another modification example of Example 7. The technologyaccording to Example 7 is applied to a TFT structure that has atwo-layer structure of a wire layer and an inter-layer film and has thesame structure as the TFT structure according to Example 4 shown in FIG.9.

[Structure]

FIG. 16 is a sectional view showing a TFT structure according to Example10. The TFT structure according to Example 10 includes the TFT 80 withthe bottom gate structure and the TFT 90 including the dummy gateelectrode 91 as in the TFT structure according to Example 4. In Example10, the technology according to Example 9 is applied to the TFT 90, Byapplying the technology according to Example 9, the top gate electrode95 is added later to the TFT 90 in a laser repairing process after thearray test. The TFT 90 has the top gate structure by adding the top gateelectrode 95. FIG. 16 shows the TFT structure after the top gateelectrode 95 indicated by a dotted line is added.

FIG. 17 is a plan view showing a TFT structure according to Example 10.FIG. 17 shows only the bottom gate electrode 81, the dummy gateelectrode 91, the top gate electrode 95, the channel regions 82 and 92,the LDD regions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2), the sourceor drain regions 84 _(_1), 84 _(_2), 94 _(_1) and 94 _(_2), the contactportions 15 _(_2), 15 _(_3), 54 _(_2), and 54 _(_3) and the wires 14_(_2), 14 _(_3), 14 _(_4), 51 _(_3), and 51 _(_4) which are constituentlayers of the TFT.

A disconnection process is performed using a laser repairing technologyon the TFT 80 with the bottom gate structure determined to have acritical defect such as leakage between a source and a drain in an arraytest. A laser repair site of disconnection from the TFT 80 is indicatedby a dotted line Y in FIG. 17. The laser repairing disconnection may beperformed on the source or drain region 84 _(_1) or 84 _(_2) of the TFT80, the bottom gate electrode 81, or one of the wire 14 _(_3) connectedto the bottom gate electrode 81 via the contact portion 15 _(_3) and thewire 51 _(_3) connected to the wire 14 _(_3) via the contact portion 54_(_2).

The top gate electrode 95 is connected to the first wire 14 _(_4)supplying a gate voltage of the TFT 90 via the second wire 51 _(_4) andthe contact portion 54 _(_3). Since the gate electrode (bottom gateelectrode) 91 is a dummy gate electrode, the TFT 90 has the top gatestructure. The top gate electrode 95 may have the same potential as thebottom gate electrode 81. The TFTs 80 and 90A are connected in parallel.Accordingly, after the laser repairing disconnection from the TFT 80 andthe formation of the top gate electrode 95 of the TFT 90, the elementcharacteristics of the TFT 108 constituted by parallel connection of theTFTs 80 and 90 are identical to the characteristics of the TFT 90A.

[Manufacturing Method]

Portions from the bottom gate electrode 81 and the dummy gate electrode91 to the wire layer including the wires 51 _(_1) and 51 _(_2) areformed through the same processes as those of Example 4. Unlike Example4, when the wire layer including the wires 51 _(_1) and 51 _(_2) isformed, the top gate electrode 95 is not yet formed.

In a step of forming the TFT 80 with the bottom gate structure, thearray test for determining the pixel characteristics is performed tospecify the TFT 80 which does not satisfy the desired characteristics,for example, the TFT 80 with the bottom gate structure which has acritical defect such as a leakage between a source and a drain. Thearray test and the laser repairing may be performed after the wire layerincluding the wires 51 _(_1) and 51 _(_2) is formed, as in Example 8.

Subsequently, a metal film of W or the like is formed only in a site inwhich the top gate electrode 95 of the TFT 90 is disposed according to alaser CVD method or using a gold paste or the like to form the top gateelectrode 95 so that a film thickness is about 50 to 500 [nm]. At thistime, the top gate electrode 95 is formed so that the channel region 92is contained in a plan view. Accordingly, the top gate electrode 95functions as the top gate electrode of the TFT 90. After the top gateelectrode 95 is formed, portions from the inter-layer film 53 to thepixel electrode 17 are formed through the same processes as those ofExample 4.

As described above, as in Example 4, the method of manufacturing the TFTstructure according to Example 10 includes the process of forming thebottom gate electrode 81 and the dummy gate electrode 91, the process offorming the polysilicon layer 61 which is the semiconductor layer, theprocess of forming the gate insulation film 12 between both of thebottom gate electrode 81 and the dummy gate electrode 91, andpolysilicon layer 61, and the process of forming the first wire layerincluding the wires 14 _(_1) and 14 _(_2) and the inter-layer insulationfilm 13 on the polysilicon layer 61. Further, the method includes theprocess of forming the contact hole (opening hole) 15B in theinter-layer insulation film 13 and the process of forming the secondwire layer including the wires 51 _(_1) and 51 _(_2) and the firstinter-layer film 16 on the first wire layer and the process of formingthe second inter-layer film 53 and the pixel electrode 17 on the secondwire layer. Above the dummy gate electrode 91 to which no potential issupplied in a layer below the channel region 92 connected to the sourceor drain region 84 _(_2) of the TFT 80 disconnected in the laserrepairing process, the top gate electrode 95 is formed in the same layeras the second wire layer including the wires 51 _(_1) and 51 _(_2) withthe channel region 92 interposed therebetween so that the channel region92 is contained in a plan view.

[Advantageous Effect]

In the TFT structure according to Example 10, after pixel darkening isperformed once by fracturing the TFT 80 with the bottom gate structuredetermined to have a critical defect such as a leakage between a sourceand a drain, the top gate electrode 95 is added to the redundant TFT 90connected in parallel to the TFT 80 in the same layer as the second wirelayer including the wires 51 _(_1) and 51 _(_2). Accordingly, since theTFT 90 functions as the TFT with the top gate structure, for example, apixel with a bright spot defect caused in the TFT 80 with the bottomgate structure having a critical defect such as leakage between a sourceand a drain can be rescued.

Description of Third Embodiment

A third embodiment is a modification example of the first embodiment.The third embodiment is the same as the first embodiment in that the TFT80 with the bottom gate structure and the TFT 90 with the top gatestructure are included on the same glass substrate 11 and the top gateelectrode 95 of the TFT 90 is provided in the same layer as the wirelayer including the wires 14 _(_1) and 14 _(_2). However, the thirdembodiment is different from the first embodiment in that the TFT 90does not include the dummy gate electrode 91. Hereinafter, a specificexample will be described as Example 11.

Example 11

[Structure]

FIG. 18 is a sectional view showing a TFT structure according toExample 1. In FIG. 18, the TFT 80 with the bottom gate structure and theTFT 90 with the top gate structure are provided on an insulationtransparent substrate, for example, the glass substrate 11.

The TFT 80 with the bottom gate structure includes the bottom gateelectrode 81 provided on the glass substrate 11, the channel region 82provided to face the bottom gate electrode 81 via the gate insulationfilm 12, and the LTD regions 83 _(_1) and 83 _(_2) and the source ordrain regions 84 _(_1) and 84 _(_2) provided on both sides of thechannel region 82. The inter-layer insulation film 13 is provided on thechannel region 82, the LDD regions 83 _(_1) and 83 _(_2), and the sourceor drain regions 84 _(_1) and 84 _(_2). The wires 14 _(_1) and 14 _(_2)are provided on the inter-layer insulation film 13. The wires 14 _(_1)and 14 _(_2) are electrically connected to the source or drain regions84 _(_1) and 84 _(_2) via the contact portions 15 _(_1) and 15 _(_2)provided to penetrate through the inter-layer insulation film 13.

The TFT 90 with the top gate structure is provided on the glasssubstrate 11, as in the bottom gate electrode 81. The TFT 90 with thetop gate structure includes the channel region 92 provided on the gateinsulation film 12, the regions 93 _(_1) and 93 _(_2) and the source ordrain regions 94 _(_1) and 94 _(_2) provided on both sides of thechannel region 92, and the top gate electrode 95 provided on theinter-layer insulation film 13 to face the channel region 92. The topgate electrode 95 is provided in the same layer as a wire layer in whichthe wires 14 _(_1) and 14 _(_2) are formed.

The wire layer including the wires 14 _(_1) and 14 _(_2) and the topgate electrode 95 are covered with the inter-layer film 16. The pixelelectrode 17 is provided on the inter-layer film 16. The pixel electrode17 is electrically connected to the wire 51 _(_2) via the contactportion 18 provided to penetrate through the inter-layer film 16.

FIG. 19 is a plan view showing a TFT structure according to Example 11.FIG. 19 shows only the bottom gate electrode 81, the top gate electrode95, the channel regions 82 and 92, the LDD regions 83 _(_1), 83 _(_2),93 _(_1), and 93 ₂ the source or drain regions 84 _(_1), 84 _(_2), 94_(_1), and 94 _(_2), the contact portions 15 _(_1), 15 _(_2), and 15_(_3), and the wires 14 _(_1), 14 _(_2), and 14 _(_3) which areconstituent layers of the TFT.

The top gate electrode 95 of the TFT 90 with the top gate structure isintegrated by extending from the wire 14 _(_1) connected to the contactportion 15 _(_1) to one source or drain region 84 _(_1) of the TFT 80with the bottom gate structure. In addition, the bottom gate electrode81 of the TFT 80 with the bottom gate structure functions as a gateelectrode by supplying a potential via the wire 14 _(_3) and the contactportion 15 _(_3).

[Manufacturing Method]

Next, a method of manufacturing the TFT structure according to Example11 will be described with reference to process diagrams of FIGS. 20A to20C.

(Process of FIG. 20A)

The bottom gate electrode 81 is formed by forming a metal film of Mo, W,Al, Ti, Cu, or the like or an alloy thin film of the metal which becomesthe bottom gate electrode 81 on the glass substrate 11 so that a thinthickness is about 10 to 500 [nm] according to a method such as asputtering method and performing a patterning process. That is, unlikeExample 1, the bottom gate electrode 91 (see FIG. 5A) is not formed.

Next, the gate insulation film 12 is formed by forming a silicon oxidefilm, a silicon nitride film, or a laminated film of a silicon oxidefilm and a silicon nitride film so that a thin thickness is about 20 to500 [nm] according to a method such as a CVD method. Thereafter, anamorphous silicon layer is formed on the gate insulation film 12 so thata film thickness is about 20 to 200 [nm] according to a method such as aCVD method and the amorphous silicon is crystallized using ELA or thelike. Subsequently, the polysilicon layer 61 which becomes the channelregions 82 and 92 is formed by performing appropriate impurityimplantation. The polysilicon layer 61 may be directly formed accordingto CVD without performing the ELA.

(Process of FIG. 20B)

Next, a photoresist 62 is applied to perform a lithography process fromthe upper surface direction of the glass substrate 11 and patterning isperformed on the photoresist 62. Subsequently, the channel regions 82and 92 of the TFTs 80 and 90 are formed by performing necessary impurityimplantation using the patterned photoresist 62 as a mask. As in Example1, back exposure may be performed on the channel region 82 using thebottom gate electrode 81.

(Process of FIG. 20C)

Next, the LDD regions 83 _(_1), 83 _(_2), 93 _(_1), and 93 _(_2) and thesource or drain regions 84 _(_1), 84 _(_2), 94 _(_1) and 94 _(_2) of theTFTs 80 and 90 are formed by performing an appropriate lithographyprocess and impurity implantation. Thereafter, the TFT 80 with thebottom gate structure and the TFT 90 with the top gate structure areformed by separating the semiconductor layer through an impurityactivation process and a process of patterning the polysilicon layer 61.

Subsequent processes will be described with reference to FIG. 18. Afterthe TFT 80 with the bottom gate structure and the TFT 90 with the topgate structure are formed, the inter-layer insulation film 13 is formedby forming a silicon oxide film, a silicon nitride film, or a laminatedfilm of a silicon oxide film and a silicon nitride film so that a filmthickness is about 50 to 1500 [nm] according to a method such as a CVDmethod. Subsequently, the contact portions 15 _(_1), 15 _(_2), and 15_(_3) including the contact holes that penetrate through the inter-layerinsulation film 13 are formed through a patterning process. Then, makingcontact to the semiconductor layer (the source or drain regions 84 _(_1)and 84 _(_2)) via the contact portions 15 _(_1) and 15 _(_2) isperformed and contact to the bottom gate electrode 81 by the contactportion 15 _(_3) is simultaneously performed (see FIG. 19).

Subsequently, a metal film of Mo, W, Al, Ti, Cu, or the like or an alloyfilm of the metal film of about 100 to 1500 [nm] is formed on theinter-layer insulation film 13 and the contact portions 15 _(_1), 15_(_2), and 15 _(_3) according to a method such as a sputtering method.Thereafter, the wires 14 _(_1) and 14 _(_2) and the top gate electrode95 are integrated through a patterning process. Next, the inter-layerfilm 16 is formed on the inter-layer insulation film 13 using siliconoxide, silicon nitride, or a photosensitive resin such as polyimide sothat a film thickness is about 200 to 3000 [nm] according to a methodsuch as a CVD method or a spin coating method. A laminated film formedof two or more kinds of films may be used in the inter-layer film 16.Next, the contact portion 18 including a contact hole penetratingthrough the inter-layer film 16 is formed through a patterning process.Next, a metal film is formed using a sputtering method or the like andthe pixel electrode 17 is formed through a patterning process.

As described above, as in Example 1, the method of manufacturing the TFTstructure according to Example 11 includes a process of forming thebottom gate electrode 81, a process of forming the polysilicon layer 61,the process of forming the gate insulation film 12 between both of thebottom gate electrode 81 and the polysilicon layer 61, and the processof forming the wire layer including the wires 14 _(_1) and 14 _(_2) andthe inter-layer insulation film 13 on the polysilicon layer 61.

Further, the method includes the process of forming the inter-layer film16 and the wire layer including the pixel electrode 17 on the wire layerincluding the wires 14 _(_1) and 14 ₂. Then, lithography patterning isperformed on the channel region 92 and the LDD regions 93 _(_1) and 93_(_2) without depending on self-alignment from a bottom gate pattern,and the top gate electrode 95 is formed in the same layer as the wirelayer including the wires 14 _(_1) and 14 _(_2) so that the channelregion 92 is contained in a plan view.[Advantageous Effect]

In the TFT structure according to Example 11, as in the TFT structureaccording to Example 1, it is possible to obtain an operational effectand advantageous effect such as separate generation of elementcharacteristics between the TFTs 80 and 90 without adding a process, asin a case in which a method of changing density of ion implantation isused. Further, since a dummy gate electrode for forming the LDD regions93 _(_1) and 93 _(_2) of the TFT 90 with the top gate structure is notnecessary, it is possible to improve the degree of freedom of layoutmore than in the TFT structure including the dummy gate electrode 91according to Example 1.

In Example 11, the TFTs 80 and 90 can be configured to be connected inseries as in Example 2 or the TFTs 80 and 90 can also be configured tobe connected in parallel as in Example 3.

<Electronic Apparatus>

The display device according to the above-described present disclosurecan be used as any of display units (display devices) of electronicapparatuses in all fields that display video signal input to electronicapparatuses or video signals generated in electronic apparatuses asimages or videos. For example, the display device can be used as any ofdisplay units of electronic apparatuses such as a television set, adigital camera, a note-type personal computer, a portable terminalapparatus such as a smartphone or a mobile phone, and a video camera.

In this way, by using the display device according to the presentdisclosure as a display unit of any of electronic apparatuses in anyfield, it is possible to obtain the following advantageous effects. Thatis, the element characteristics are able to be separately generatedwithout adding processes according to the technology of the presentdisclosure. Therefore, it is possible to achieve an improvement inimage-quality performance without increasing cost. In addition, sincefootprints can be reduced, it is possible to achieve miniaturization ofan electronic apparatus.

The display device according to the present disclosure also has a moduleform configured to be sealed. For example, the module corresponds to adisplay module formed such that a facing unit such as a transparentglass is attached to a pixel array unit. In the display module, acircuit unit or a flexible printed circuit (FPC) that inputs and outputssignals or the like between the outside and the pixel array unit may beprovided. Hereinafter, smartphones are exemplified as specific examplesof an electronic apparatus using the display device according to thepresent disclosure. Here, the specific examples exemplified here aremerely examples and the present disclosure is not limited thereto.

Specific Example

FIGS. 21A and 21B are external views showing smartphones which areexamples of electronic apparatuses according to the present disclosure.Smartphones 200A and 200B each include a display unit 210 and amanipulation unit 220. In the case of the smartphone 200A shown in FIG.21A, the manipulation unit 220 is provided below the display unit 210 ofa casing 230. In the case of the smartphone 200B shown in FIG. 21B, themanipulation unit 220 is provided on an upper surface of the displayunit 210 of a casing 230. The display device according to the presentdisclosure can be used as the display units 210 of the smartphones 200Aand 200B. That is, the smartphones 200A and 200B according to thespecific examples are manufactured using the display device according tothe present disclosure as the display units 210.

As described above, by using the display device according to the presentdisclosure as the display units 210 of the smartphones 200A and 200B,the element characteristics are able to be separately generated withoutadding processes. Therefore, it is possible to achieve an improvement inimage-quality performance without increasing cost. In addition, sincefootprints can be reduced, it is possible to achieve miniaturization ofsmartphones 200A and 200B.

Additionally, the present technology may also be configured as below.

[1]

A display device including:

a thin film transistor with a bottom gate structure and a thin filmtransistor with a top gate structure on a same substrate,

wherein a top gate electrode of the thin film transistor with the topgate structure is provided in a same layer as a wire layer.

[2]

The display device according to [1],

wherein the top gate electrode of the thin film transistor with the topgate structure is integrated by extending from a wire electricallyconnected to a source or drain region of the thin film transistor of thebottom gate structure.

[3]

The display device according to [1] or [2],

wherein the thin film transistor with the top gate structure includes adummy gate electrode in a floating state.

[4]

The display device according to any of [1] to [3],

wherein the wire layer in which the top gate structure is provided is afirst wire layer provided on an inter-layer insulation film on the thinfilm transistor.

[5]

The display device according to any of [1] to [4],

wherein a first wire layer is provided on an inter-layer insulation filmon the thin film transistor and a first inter-layer film is provided onthe first wire layer, and

the wire layer in which the top gate structure is provided is a secondwire layer provided on the first inter-layer film.

[6]

The display device according to [5],

wherein a contact hole is formed in a site of the inter-layer insulationfilm corresponding to a channel region of the thin film transistor withthe top gate structure, and

a gate insulation film is provided on the inter-layer insulation filmcontaining the contact hole.

[7]

The display device according to [6],

wherein the gate insulation film is constituted by a high dielectricinter-layer film.

[8]

The display device according to [6] or [7],

wherein the contact hole is formed in a site of the first inter-layerfilm corresponding to the thin film transistor with the top gatestructure, and

the top gate electrode of the thin film transistor with the top gatestructure is provided in a same layer as a second wire layer on thefirst inter-layer film, in the contact hole, and on the gate insulationfilm.

[9]

The display device according to [8],

wherein the top gate electrode of the thin film transistor with the topgate structure is disposed to face a channel region of the thin filmtransistor via the gate insulation film constituted by a high dielectricinter-layer film.

[10]

The display device according to any of [1] to [9],

wherein the thin film transistor with the bottom gate structure and thethin film transistor with the top gate structure are connected in seriesfor use.

[11]

The display device according to any of [1] to [9],

wherein the thin film transistor with the bottom gate structure and thethin film transistor with the top gate structure are connected inparallel for use.

[12]

The display device according to [10] or [11],

wherein a source or drain region of the thin film transistor with thebottom gate structure is connected directly to a source or drain regionof the thin film transistor with the top gate structure without passingthrough a wire layer.

[13]

The display device according to any of [10] to [12],

wherein a bottom gate electrode of the thin film transistor with thebottom gate structure and the top gate electrode of the thin filmtransistor with the top gate structure have a same potential.

[14]

The display device according to any of [1] to [13],

wherein a unit pixel including a light emission unit is disposed to beconstituted, and

the unit pixel includes a writing transistor that writes a signal and adrive transistor that drives the light emission unit based on the signalwritten by the writing transistor,

-   -   wherein the writing transistor is constituted by the thin film        transistor with the bottom gate structure, and    -   the drive transistor is constituted by e thin film transistor        with the top gate structure.        [15]

A method of manufacturing a display device that includes a thin filmtransistor with a bottom gate structure and a thin film transistor witha top gate structure on a same substrate, the method including:

forming a top gate electrode of the thin film transistor with the topgate structure in a same layer as a wire layer.

[16]

A method of manufacturing a display device, the method including:

performing an array test to determine element characteristics of anindividual thin film transistor in a step of forming a thin filmtransistor with a bottom gate structure; and

forming a top gate electrode in a same layer as a wire layer in regardto the thin film transistor with the bottom gate structure in order torepair a pixel including a thin film transistor determined to be worsethan predetermined characteristics.

[17]

The method of manufacturing a display device according to [16],

wherein the top gate electrode is formed using a method of connecting awire by forming a metal thin film in accordance with a CVD method.

[18]

The method of manufacturing a display device according to [16] or [17],

wherein the thin film transistor in which the top gate electrode isformed is a repairing target thin film transistor determined to be worsethan predetermined characteristics, and

the top gate electrodes is formed to face a bottom gate electrode of therepairing target thin film transistor with a channel region interposedtherebetween.

[19]

The method of manufacturing a display device according to [16] or [17],

wherein the thin film transistor in which the top gate electrode isformed is another thin film transistor that is provided on a samesubstrate as a repairing target thin film transistor determined to beworse than predetermined characteristics and connected in parallel tothe repairing target thin film transistor, and

the top gate electrodes is disposed to face a bottom gate electrode ofthe other thin film transistor with a channel region interposedtherebetween.

[20]

An electronic apparatus including:

a display device which includes a thin film transistor with a bottomgate structure and a thin film transistor with a top gate structure on asame substrate and in which a top gate electrode of the thin filmtransistor with the top gate structure is provided in a same layer as awire layer.

REFERENCE SIGNS LIST

-   10 organic EL display device-   11 glass substrate-   12 gate insulation film-   13 inter-layer insulation film-   14 _(_1) to 14 ₋₄ wires of first wire layer-   15 _(_1) to 15 _(_4), 18, 19 ₋₀, 19 ₋₁, 19 ₋₂ contact portions-   16 first inter-layer film-   16A, 16B contact hole-   17 pixel electrode-   20 unit pixel (pixel circuit)-   21 organic EL element-   22 drive transistor-   23 writing transistor-   24 retention capacitor-   25 auxiliary capacitor-   30 pixel array unit-   31 (31 ₁ to 31 _(m)) scanning lines-   32 (32 ₁ to 32 _(m)) power supply lines-   33 (33 ₁ to 33 _(n)) signal lines-   34 common power supply line-   40 write scanning line-   50 power supply scanning unit-   51 _(_1) to 51 ₋₄ wires of second wire layer-   52 gate insulation film-   52A contact hole-   53 second inter-layer film-   54 _(_1) to 54 _(_3) contact portions-   60 signal output unit-   61 polysilicon layer-   62 photoresist-   70 display panel-   80 TFT with bottom gate structure-   81, 91′ bottom gate electrode-   82 channel region-   83 _(_1), 83 _(_2) LDD region-   84 _(_1), 84 _(_2) source or drain region-   85 top gate electrode-   90 TFT with top gate structure-   91 dummy gate electrode-   92 channel region-   93 _(_1), 93 _(_2) LDD region-   94 _(_1), 94 _(_2) source or drain region-   95 top gate electrode

The invention claimed is:
 1. A display device comprising: a substrate;and a plurality of pixels arranged on the substrate, respective ones ofthe plurality of pixels including a light emitting element, a drivingtransistor, a sampling transistor and a capacitor, wherein the lightemitting element includes a first electrode, an organic layer disposedon the first electrode, and a second electrode disposed on the organiclayer, the driving transistor includes a first gate electrode and afirst semiconductor layer, and the first semiconductor layer beingdisposed between the first gate electrode and a first metal layer, thesampling transistor includes a second gate electrode and a secondsemiconductor layer, a first wiring is electrically connected to thefirst electrode of the light emitting element, the first gate electrodeand the first wiring are disposed at a second metal layer different fromthe first metal layer, the first semiconductor layer and the secondsemiconductor layer are distinct from each other.
 2. The display deviceaccording to claim 1, wherein the first metal layer of the drivingtransistor is a dummy gate electrode of the driving transistor.
 3. Thedisplay device according to claim 2, wherein the dummy gate electrode isdisconnected from a supply of a predetermined potential.
 4. The displaydevice according to claim 1, wherein the second gate electrode isdisposed between the substrate and the second semiconductor layer. 5.The display device according to claim 1, wherein a second wiring iselectrically connected to the second semiconductor layer.
 6. The displaydevice according to claim 5, wherein the second wiring is disposed at alevel of the second metal layer.
 7. The display device according toclaim 1, wherein the first gate electrode of the first transistor isconnected to an electrode of the capacitor.
 8. The display deviceaccording to claim 1, wherein the first electrode is overlapped with achannel region of the driving transistor in a cross-sectional view. 9.The display device according to claim 8, wherein the first electrode isoverlapped with a channel region of the sampling transistor in thecross-sectional view.
 10. The display device according to claim 1,wherein the first electrode is overlapped with a channel region of thesampling transistor in a cross-sectional view.